I’ve noticed that on my iPhone 6 Plus running iOS 9, the user interface is very laggy for me to the point where I’ve regretted updating. I’ve also noticed the issue on the 6S Plus, but mainly when you 3D touch things. I made this video before I noticed but doing this fixes that as well. From what I’ve seen it looks like the lag is mainly with the 6 Plus, while other devices perform better (e.g. iPhone 5, 5c, 5s, 6). I found a way to vastly improve the performance so animations and load times are much faster and smoother.