This is usually a bad approach! The “normal” workflow is to model anything in separated files. I don't believe that a room with nothing in it will need 7.000.000 polys for just walls and a door so remove anything that isn't part of the room architecture to separate files. Those are then assembled t…

How much memory does your PC have, and are you running a 64-bit version of 3DS Max? That seems a remarkably low polycount for the software to be crashing.

Although, as frob suggests, you are going to have trouble displaying all those polys in a game. You'll likely need to decimate the mesh and bake …