Hey, i recently have some problems with low FPS after update to Unity 5 on Windows Phone 8.1. On PC or Android everything worked fine. I searched internet and found that other people have simmilar issues. The whole thread is here
“Similar issue. One of my games runs at 24-30 FPS on i9003 in Unity 4.6 but with 5.0 its down to 6-7 FPS. I was hoping for FPS improvement with GPU skinning and Static batching being made available to all but this is disappointing.”
– so just disable Static batching and everything in my case works fine now.