I agree with fireside. 259,000 faces may be low-poly by animation standards (I wouldn’t know), but it is so far from low-poly by game standards that it’s almost crazy. Remeber, the game engine calculates faces in triangles, not quadrilaterals, so if any of your faces are quads in your models, they count as two tris in the game engine. You could have anywhere up to almost 520,000 tris in that file! The general consensus around here seems to be that 25,000 to 40,000 is about the max number of faces you can use (per scene) running Blender’s default renderer (ketsji). Depending on your graphics card, you may be able to run the file with snailrose’s OGRE implementation (alpah release). That should increase frame rate, but I doubt it will help with load time. (Run a search on the Game Engine board for “OGRE” to find it.)
I’m not exactly sure how the program will run, but fireside is right about separate scenes as well. Will the user begin exploring from outside and select the house model to enter? Then use fireside’s suggestion of loading the insides as the user enters/approaches. If all seven houses do not need to be displayed at once, then you can put each house in a separate scene and allow the user to select each one individually via a menu.
Hope that helps.