Building Light Cache Vray suddenly took too long

I am working on a bedroom scene when all was going fine. Until halfway throughout the work process, I tried to do an Interactive Render and suddenly the render went extremely slow at the building light cache part, which took around 2 mins to load.
What happenend with the file?

In this file, i went on and removed almost all the models and left the walls only. But the problem is still there?
1ST FLOOR 3D(a).skp (1.7 MB)

Are you working in VRay? It would help if you stated this in your post.

Yes. I am working in VRay