As it's a sealed room, why even bother with having the construct in the scene? Just delete it using the hierarchy editor. This example is illuminated only by the ceiling lights with the ambient set to 10, so no need to use what looks like a point light reflected in the mirror to light the scene. You can also use Snarly's SceneFixer to remove ambient from everything in the scene, then you can manually add ambient to just the materials you want.

These were the render settings I used.