Late response here, you were responding to how I thought the iPhone 6 felt like a performance regression. I was also coming from a 4s running iOS 8, of course it was faster than that. But still, the iPhone 6 felt slow for being the newest iPhone. It was definitely slower than my wife's iPhone 5s which was running iOS 7 at the time, so maybe iOS 8 is to blame, but maybe also having to render to a larger screen was a factor.