Dont forget you can use differing models for walls, ceilings and so on that are created when needed and destroyed when not needed so that your house looks fine from any camera view but isn't really a high poly count soup.

A bit more work and an increase in the distributed files but good frame rates.

And then doing the same for complete rooms that are only single level structures created when your player enters and so on.

Look for work-a-rounds in every conceivable situation or think about how athers may have acheived the very same effect you are looking for.

Personally, I would create a very high poly count to test for looks and maybe keep using it without a LOD system untill I was sure the coding worked flawlessly then and only then would I look at creating true game assetts as my previouse posted test files has shown in the Borderline Conflict and Middle Earth series.

Being astute in the use of a LOD system like above can actually be incorporated to make levels look bigger too...and such a system was once posted so could still be in archieves yet.

Dont think I'm offering the only way to do things here, its just another approach to consider.