Change HTC Vive compositor progress panel image

I know this was asked a while ago but I'll throw this in here as I was thinking about something similar and came across this in a search.

This isn't easy, however, I would start by asking whether an alternative thought process is required. You can create a fairly simple adaptive quality script that spots when you are not getting the frame rate you require and then adjusts using

 UnityEngine.XR.XRSettings.renderViewportScale = betterScale;
 QualitySettings.SetQualityLevel(betterQualityLevel, false);

I appreciate that is obtuse enough to be next to useless, but the scripts to implement that aren't too complex, you can find my scripts here AdaptiveQuality.cs and here AdaptiveViewport.cs. Note this last script goes on your main camera in the scene.

If that still doesn't work for you then the SteamVR_LoadLevel script is actually quite useful to pick through. As it does do what you need. Again based on some form of adaptive quality script, you can use the elements in that script to achieve what you need. The basic format is

 Generate Loading Screen
 Setup Loading Screen Overlay 
 Load a SkyBox
 SteamVR_Render.pauseRendering = true
 Fade in the Loading Screen/Skybox
 SteamVR_Render.pauseRendering = false
 Fade out the overlays, fade in the screen you need

However, I would also be asking the question as to why the frame rate drops given that would be where I would start looking at improvements.