I've used my mini for two years and been running super fast and effective and immediately after iOS 9 it's a slug . I even wiped it and it's still sluggish wtf apple
Did you update via Wifi? Maybe a bad install file. Factory reset it and install iOS9 again with a PC.
Do you have an email address with thousands of content? I had to install the gmail app for my wife's iOS9 iphone5 because of that. Apparently, iOS9 will check through your entire emails and prepare search results and suggestions if the need arises.
I was just thinking I'll iodate my mini 1 today because I haven't read any negative comments yet. I'll hold iff now to see if you manage to improve yours with the email tweak.