iOS 9 runs slow and flakey for some iPad 2 users.
I am running iOS 9.3.5 and is running pretty well on it.
But I seem to be part of a small majority of iPad 2 users who haven't run into too many performance issues with iOS 9.
My ONLY explanation seems to be that I completely skipped iOS 8 on all of my iDevices because I didn't like it and it offered no compelling features for any of my iDevices.
So, whatever was wrong or buggy with iOS 8 it never got worse when I finally decided to upgrade to iOS 9 as I never installed iOS 8 on any of my iDevices.
As I stated earlier, some iPad 2 models didn't like iOS 9.
Especially the 16 GB storage models when users have run down the free data storage to 2 GBs and less.
If your iPad 2 is still running fine with iOS 8 and your devices is still receiving app updates, forget about upgrading to iOS 9 and put off having to upgrade to iOS 9 for as long as possible.
Keep your iPad 2 on iOS 8.4.
Good Luck!