IOS load up bug

Whenever I load up Minecraft, it freezes up and then lags very badly when I'm using my Iphone's data. It only ever works properly when I'm connected to WiFi. The issue with that is, I usually can't use WiFi at the moment so it becomes very difficult to try and load up Minecraft. It gets too laggy to the point it crashes.

(This is my first time reporting a bug so I hope I wasn't too hard to follow.)