I took the video from my iPad 4. I don't even know where or what to do or use to speed up my video even if I wanted to go through that trouble. I'm on 8.4.1. There is no public jailbreak for it available yet. I don't have bionic fingers. Maybe I'll post another video later again with my iPad. It's just such a PITA because I have to hold it and use my phone at the same time that's why the video was a little shaky.
Chill out man 8.4.1 is more responsive than iOS 9. It's just a fact. Even a 6S wouldn't be able to react as fast because of iOS 9 holding it back by making you wait for animations to be over.
It seems pretty clear to me that you haven't used iOS 8 on your iPhone 6 very much. You'd remember the feel and speed otherwise.