I agree. The Mini 2 is certainly faster, but the iPad 2 stutters less predictably. I feel its something to do with 64 bit iPads... The iPad 4 I think is reasonable?
The way I see it is that the iPad 2 didn't really get jittery till iOS 8.0 (there was a bit in 7.0, but that was rectified with 7.1). So it got through its first and second updates (5.0, 6.0) with no problems, where as the Mini 2 is on its FIRST update and already a jittery mess.
I've found that 8.3 made my Mini 2 even worse, but generally sped up my iPad 2 ,so I actually prefer to use my iPad 2 at the moment, as it does some jitters, but they are not predictable and I know its because the iPad 2 is 4 years old its semi acceptable.
Whats even crazier is that this would be the same on the iPad Mini 3 as it have the same internals as the iPad Mini 2 - so essentially their top of the line mini must be a wreck as well.
It really annoys me that iOS 8 is such a wreck. Was iOS 7 the same? I only bought the Mini 2 a month ago so I didn't experience iOS 7 on it