I have been noticing quite a bit of stutter as well
During safari. App switching.
The big one that is easily noticeable is switching split and locked keyboard, When dragging it apart or together it really stutters and the animation is quite bad.
Keyboard has been jacked since iOS 8. iOS 8.0 betas introduced a bug where the split keyboard got graphical glitches (and lags) while splitting or moving. Using the device (scrolling up and down safari) with a split keyboard stutters tremendously, while scrolling has normal performance with the normal keyboard.
Also the bug was introduced that involves the keyboard and Reduce Transparency. If you turn that setting on, there are no key-tap indicators on the light keyboard, dark keyboard is unaffected though.
Oh also, iOS 8 introduced a bug where split keyboards are connected when they pop up at first, then when the animation finishes it abruptly disappears and it looks weird.
I've reported ALL of these bugs to Apple since iOS 8, tons of times through iOS 9 and there have been no responses or bug fixes. Apple doesn't care.
iOS 7 had none of these issues. In fact, the split keyboard was way smoother than the regular one back then on my mini 2. You could have a consistent 60fps keyboard rotation animation with the split keyboard, however with the normal keyboard, stuttery and sluggish like usual. That made sense because less was being blurred, however now it's backwards of what it should be in terms of performance because of shoddy coding.
I don't think I will ever buy another iPad as long as iOS has these stupid inefficiencies. I may as well get a $400 iPad Air 2 if the much more powerful $600 iPad Pro will have all the same stutters due to bad software.