I had auto install for update but the current one is still 12.5.5. How do I get iso 15 from iso 12?

It is highly possible that your iPad year and model may not be able to upgrade/update beyond any version of iOS 12, currently at iOS 12.5.5.

The 2013 iPad Air 1 ( “A” model number A1474/1475/1476 ), iPad Mini 2 ( “ A” model number A1489/1490/1491 ) and the 2014 iPad Mini 3 ( “A” model number A1599/1600/1601 ) cannot upgrade beyond any version of iOS 12.

Sorry.

These iPad models have overall internal hardware that is too old, too underpowered and incapable of running all of the new, advanced and internal hardware resource intensive features of iPadOS.

These iPad models are now 7 and 8-years old, in 2021.

Sorry.

Third party app support, typically, continues for 2-3 years AFTER Apple ends full support of a subset of their devices.

The last major update to iOS 12 was in 2019, with iOS 12.3.

So, it has been nearly two years after, already, and third party app support is already on a downward trend for all iOS 12 supported devices.

Look for many more third party apps dropping support for all iOS 12 supported devices as another year progresses.

The immediately above statement is what you really need to worry about.

Sorry.

There is one last thing you can try/attempt, if you need older versions of apps.

If you own another much newer iOS device that can run iOS/iPadOS 13 and later, you can install the most recent version app/s onto that more recent iOS device.

Then go back to your older iPad, open the iOS App Store, go to the Purchases section of the store app, search for the app/s you wish to try and download to that older iPad and see if an older version of the app is allowed to be downloaded/installed to that older iPad.

These newer iOS/iPadOS devices must use your same Apple ID user account and password.

Failing that OR IF NO joy, then there is nothing more to be done.

It's 2021, now.

If you need/want an iPad with an up to date iPadOS with access to current, updated apps, then you really need to seriously consider a purchase of a new iPad model OR a much, MUCH “newer” and less expensive, refurbished or used iPad models, from better known, trusted sources, like other Apple product/device retailers/resellers, some locally or from online, on the Web/Internet, capable of running the latest iPadOS versions.

There are PLENTY of newer, older iPad models that can run the latest, current versions of iPadOS.

If you need OR ONLY able to purchase older, less expensive iPad models, look at older IPads from 2014 and later.

All of these older model iPads below CAN run the latest iPadOS versions and the up and coming iPadOS 15.

2014, 9,7 inch screen iPad Air 2 models

2015, 7.9 inch screen iPad Mini 4 models

2015-2017, 12.9 inch screen iPad Pro models. ( 1st gen Pencil support )

2016, 9.7 inch screen iPad Pro models ( 1st gen Pencil support )

2017, 10.5 inch screen iPad Pro models ( 1st gen Pencil support )

2017, 9.7 inch screen iPad 5th gen models

2018, 9.7 inch screen iPad 6th gen models ( 1st gen Pencil support )

2019, 10.2 inch screen iPad 7th gen models ( 1st gen Pencil support )

2020, 10.2 inch screen iPad 8th gen models. ( 1st gen Pencil support )

Get the largest internal data storage model you can afford as NO Apple iOS device has expandable storage.

I am sorry that you had to learn all of this, but this does not change any of the facts regarding these older iOS devices.

Sorry & Best of Luck to You!

The first generation iPad Air, iPad mini2 and mini3 can only be updated to iOS 12.5.5. With this version installed, you will have one of these three models.

Not sure which iPad you have? Identify your iPad model.

Apple ended major update support for these models of iPad in September 2019 - although they since continue to receive “point” security updates - the most recent being released just a few days ago. These devices cannot be updated to iPadOS 13 (or any later major versions of iPadOS) as the internal hardware does not meet the minimum technical requirements (CPU and RAM) for newer versions of iOS/iPadOS.

I hope this information provides helpful and succinct clarity.

iPad Air can only run as high as iOS 12.5.5

Here's a simple and fast way to see what is possible with your device, including updating it to the highest sub-version (e.g., 14.7 --> 14.8) of an iOS/iPadOS you may already have:

On your device, tap:

Settings > General > Software Update.

1. If it says your device is up to date there is nothing more you can do. If apps you are trying to use say you need a higher iOS version, you will need to buy a newer device if you want to run those apps or features.

2. If it says an update is available you will normally only be given one update selection which will be the highest available iOS version supported by your device. However, if you are running iOS 14.5 or greater, or iOS 15 you may see two options. Click on a link below for full instructions about how to update with wi-fi or 5G, or using a computer (see links in document) if you have storage or connectivity issues. If the update listed is not equal to or higher than the iOS version you need to use a feature, you again will need to buy newer equipment if you want to use that feature.

Update your iPhone, iPad, or iPod touch wirelessly. Click here --> https://support.apple.com/HT204204

Update your iPhone, iPad, or iPod touch with the Finder [Catalina or later] --> https://support.apple.com/HT212185

Update your iPhone, iPad, or iPod touch with iTunes [Mac Mojave or earlier; Windows] --> https://support.apple.com/HT212186

Or this video:

"How to update your iPhone or iPad" click here --> https://youtu.be/csJAEyvvruY

Read all the given advice above.

You will need a new or “newer“, refurbished or secondhand used device, now.

No option.

Sorry.

If you decide to go down the path of purchasing used, secondhand Apple devices, here is how to avoid purchasing an Apple iOS/iPadOS device with user activation lock, in the future.

If you purchase any iPad, or any Apple iOS device, for that matter, used/second hand, online, or even in-person, make sure this iPad does NOT have user activation lock and has been properly reset for sale.

A properly reset for sale iPad should initially power up to an animated, multi-language “Welcome” screen.

DO NOT take the iPad seller's word that this iPad is user activation lock free,

We have seen plenty of used iOS device purchasers get scammed.

User Activation Lock can never be bypasss, circumvented or worked around IF there is no correct previous/original user information to be able to do so.

Apple doesn't get involved with ANY user activation locked, used/second-hand sold devices, either.

So, buyer beware.

If purchasing a used device in-person, power the iPad ON

If the iPad DOES NOT display the initial animated, multi-language “Welcome” screen, then pass on purchasing this iPad.

If the iPad powers up to any other screen, then forget purchasing this iPad.

You cannot trust that the seller actually has the correct needed info to properly reset the iPad back to factory settings right then and there before the actual purchase and exchange of money for the iPad, in question.

Pass on the device!

If you are purchasing this used iPad online ask the seller to provide multiple images, either online or be sent to you via email, showing this animated, multi-language “Welcome” screen of the interested in purchasing iPad model.

Even better, ask for a short video be sent to you showing this animated, multi-language “Welcome” screen, in action and in its entirety, posted to the online ad or emailed to you.

If the online iPad seller refuses any of these requests, pass on the iPad. DO NOT buy!

Good Luck to You!