Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I had an iPad mini 2 and didn't find it slow at all with iOS 8. I only used it for browsing, checking twitter, drawing things in Paper and playing the odd game.

I recently got an iPad Air 2 due to the screen size and while it's a smoother experience, the mini 2 is still a good usable device for most tasks.
 
I just purchased a mini 2 today on a similar Best Buy open-box deal (someone took advantage of that best buy deal earlier in the month, broke the shrink wrap, and brought it back). It has wonderful performance on iOS 8 for me, no slowdowns at all today.
 
I just don't understand how people can say that mini 2 is fast, IT'S NOT, with ios 8 it has almost as much lag as an iphone 4s.

you might want to try a fresh install as new

i have the mini 2 running the latest firmware and other then safari reloading,is fast
i wish it had more ram
 
I have an iPad Mini 2 and an iPhone 6 both on iOS 8. I notice no speed difference. If anything, the iPad seems faster at times.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.