I also remember reading that there are some obscure settings in iOS 9 that it is better to turn off for older iPads and that can make a big difference to performance. I don't believe I ever had them on in the first place on mine when I checked. I can't remember what those setting were - it was a few months ago that I read this - but a quick Google of 'iPad 2 slow on iOS 9' will, I think, bring up a number of suggestions. For me the suggestion that worked was a clean reinstall.
When there's an eel in the lake that's as long as a snake that's a moray.