Ipad2 either very slow or it crashes. Capacity 12.90 available space 2.7 GB. Model number DL*******KPH

Try resetting All Settings found in the Settings App under General and in the right column under Reset.
Try resetting histories and deleting/resetting caches in all of the web browsers you use.
If you use Safari, these functions maybe in the Settings App under Safari.
Other web browsers have their settings inside of the running app, itself.
If your iPad has been activated for iCloud, in the Settings App under iCloud, to the right, under iCloud Drive, tap iCloud Drive and make sure Safari is turned off for saving Safari data to iCloud Drive.
Also, under iCloud in the Settings App, in iCloud Drive, disable the saving feature for any other apps that you DO NOT want data being saved automatically to iCloud Drive.
If using Safari is still causing issues,
Try changing/using another, different third party web browser.
I don't use iOS Safari too much any longer because I found it causing me some headaches on certain websites I, regularly, visit.
I commonly use another third party web browser, Perfect Web Browser (there are others that may suit your web browsing style better, so look at all of them first to see which third party browser may work better for you) and I never experience a lot of the issues that Safari was causing.
In the Settings App under the General tab, to the right under Spotlight sesrch, try disabling the search under apps that really do not need a search, like some games, remotes, apps that really do not need to be searched, etc., to reduce the list for Spotlight to search.
Try turning on Reduced Motion.
This is found in the Settings App in the General tab the left panel.
In the right panel look under Accessibility, the look for Reduce Motion and turn this feature "On".
You should see an appreciable performance increase on all iPad 2, 3 and 4 models.
In the Settings App under the General Tab, in the right column, look for Background App Refresh and turn this setting to "off".
Try a reset of your iPad by holding down both the Home and sleep/wake buttons simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons.

Good Luck!

Most of us have things stored on our devices that are no longer needed. See if you can free up about 2GB more free space.

Failing the above or your iPad 2 isn't much faster, 2.7 GBs of available isn't much.

You really should be maintaining a minimum available free storage space of between 4-6 GBs.

If your iPad was near full (2 GBs of free storage space or less) this is but only one reason why your older iPad isn't coping well with iOS 9.
You need to backup all of your data on your iPad, either to iTunes on a computer, through Apple's own iCloud/iCloud Drive OR a dedicated Wireless WiFi hard drive, and then start deleting items off of your iPad.
You should start with paring down any music, movies and photos you may have on your iPad.
Then look at apps that you may no longer use and delete these (you can always redownload deleted apps at a later time).

Other procedure you could try if my above advice still hasn't helped enough.

First, connect your iPad to USB and sync and backup your iPad to iTunes (make sure your iTunes is up to date).

Then disconnect/eject your iPad from the computer.

From just the iPad, in the Settings App under the General setting, look in the right column for Reset option, then erase and reset your iPad to completely erase your iPad 4 and then, again, from the iPad, set it up as a new iPad setup to factory "out of the box" operation.

Then reconnect your iPad 4 to the computer and make sure to cancel the syncing, by tapping the small X to the left in the top center iTunes display box.

iTunes should detect your iPad and ask if you want to update to the latest iOS version.

Select OK. If iTunes begins to try and sync, again, cancel the sync. Let the update continue until it loads into the iPad.

May take anywhere from 30 minutes to an hour to update the iPad.

DO NOT WALK AWAY FROM THE COMPUTER DURING THE UPGRADING PROCESS!!!!

Once your iPad is updated and your iPad appears in iTunes, again, CANCEL the sync, once more.

Select Restore from Backup instead and pick your last backup to restore back to your iPad 4.

Once the restore is complete, finish setting up the iPad and let it sync back to iTunes you can either cancel the sync, again or let it backup, again.

Then disconnect the iPad.

Do one hard reset of your iPad by holding down both the Home and sleep/wake buttons simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons.

Once your iPad is back to the Home screen,

In the Settings App under the General tab, to the right under Spotlight sesrch, try disabling the search under apps that really do not need a search, like some games, remotes, apps that really do not need to be searched, etc., to reduce the list for Spotlight to search.

Try turning on Reduced Motion.

This is found in the Settings App in the General tab the left panel.

In the right panel look under Accessibility, the look for Reduce Motion and turn this feature "On".

You should see an appreciable performance increase on all iPad 2, 3 and 4 models.

In the Settings App under the General Tab, in the right column, look for Background App Refresh and turn this setting to "off".

I update ALL my iDevices connected up to my iMac and sync'd over USB through iTunes.

My Mom"s and Wife's iPad 2s were still both on iOS 7 and my own iPad 3 this way.

I have NEVER, EVER had an issue with any iOS updates.

Good Luck!

I am sooo glad this all worked out for you and your iPad 2.

I have posted all of this in other postings here and, basically, been taking a LOT of flak being toid nothing I posted has worked for them, I do not know what I am talking about and doing and lying about how well the iPad 2s I upgraded have been working, being called some sort of Apple Fanboy, or that I must be working for Apple because I am constantly defending my own actions, viewpoints, assertions and my step by step suggested fixes.

I am glad that some of my solutions worked for your circumstance.

Thank You VERY MUCH for giving me the 10 points.

I appreciate it!

Be Well...Stay Well,

😉

Michel