How can I update iOS 15 on my iPhone 6 Plus?

Sorry, but iPhone 6 Plus can be updated to iOS 12.5.7 and no higher. Your phone was released 11 years ago and it is now obsolete. If you need a higher version iOS than your phone can support, then you have to buy a new iPhone at this time.

Not happening. The iPhone 6 Plus hardware is lacking. You’ll need a newer or new iPhone.

iPhone SE 2nd, iPhone 11, or newer, would be the preferred choice here, given those have access to the upcoming iOS 26.

An iPhone 5s, iPhone 6, or iPhone 6 Plus isn't capable of 13 or above; they require at least 2GB of RAM. Try downloading the application to a newer unit on the same Apple Account first.

(261084)

junison18 wrote:

How can i get IOS 15 for my iphone 6 plus..

You cannot. The iPhone 6 Plus lacks the hardware to run iOS 13 or later. For instance, it has only 1 GB of RAM – and from what I can tell, all iPhones that can run iOS 15 have at least twice that much.

i need to install that software to download a apps in the apps store

Then you need to replace that outdated iPhone 6 Plus with a newer iPhone. I would suggest looking for one that can run iOS 18 and that will be able to run iOS 26 when it comes out this fall. Note that while an iPhone 11-series phone can do these things, iOS 26 will represent the sixth major iOS update for that phone. That suggests that it very likely is the last. An iPhone 15- or 16-series phones, or one of the iPhones that Apple is likely to release later this year, would presumably have years of iOS updates ahead of it.

If you are thinking about buying a used iPhone to "save money", please read

The All Too Common SAD Reality of Buying a Used iPad/iPhone – Apple Community

so that you know what to look for to avoid buying a useless "brick".

The iPhone 6 Plus has reached the end-of-life support for Software Updates to the latest iOS operating system, depriving you of new features created many years ago.

Many modern apps are not compatible, limiting the usability of your device.

You are invited to visit an Apple retail store to discuss your iPhone upgrade options.

Learn about the ⇢ iPhone Upgrade Program. ⇠📲

Good luck! 👋🏼😉

Note that the iPhone 6 Plus is so old that Apple does not offer anything for trading one in. (The oldest phone for which they still offer trade-in credit is the iPhone 8.)

Apple will recycle the iPhone 6 Plus free of charge.

Apple Trade In - Apple

Before recycling the iPhone 6 Plus, the OP may want to transfer data to a new phone, and then wipe the iPhone 6 Plus, as outlined in the following Support articles:

Use Quick Start to transfer data to a new iPhone or iPad - Apple Support

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Thanks for bringing that to my attention.

I will revise for future posts. 😉