Frame rate issue - VR Cardboard App for Android

Hi, We are facing a serious problem with frame rate on mobile when we run VR Cardboard app. The content is very simple. It is just a simple room (made of 6 simple polygons) and a script to move the camera in room. We see a good frame rate of around 120+ on Windows PC. When we run the same on a android mobile with 3GB RAM and Octacore processor, the frame rate drops to 30. Similar experience when we tried with Samsung Gear VR (S7 Edge) We have tested the same app on another android mobile (2GB RAM, Octacore processor) and found that frame rate is around 55. We have checked mobile settings (in developer options), tried with different VR Cardboards after calibration. We have no clue where the issue is? If there is a problem with script used, I believe it shouldn't run at 55fps on one mobile which has less RAM and at the same time run at 30fps on another mobile. Used Unity 5.5 . Explored other similar threads but could not find a solution. Request you for suggestions/solution.