Afslog as you have sufficient memory, your ok. In my Experience most problems with iPads or iPhones getting slow is a full "disk". It is a good investment to buy the products with as much memory as possible. This written from an iPad 3 running iOS 8.2
Thank you, @lars_ole. So if I use an iPad 3 64Gb, I can upgrade to iOS 8.2 without running slowly? Because the memory which I used until now is only about 30Gb.