How to profile XR.WaitForGPU GVR Cardboard Android?

When I use GVR for Cardboard with a simple scene, a lot of time is used for XR.WaitForGPU. Is there a way to find out what's going on there?

I tested the scene with the LWRP, the most minimal settings and following option, to make sure there isn't a lot of work for the GPU, but the result is always a waiting time between 4-12ms.

Code (CSharp):

1.  XRSettings.renderViewportScale = 0.1f;
2.  

The goal is to make in between scenes, so the smartphone can cool down, during some menu scenes.