1.you got toom much detail dude, its nice that you put stuff in the closets, drawers and such, but dont spam in there
2. try not to use to many round/organic items, they use many more polygons(tris) and thats just how it is, so when you can get away with it, still having the scene look pretty use some more blocky objects.
3. Try to use static objects, or generally just objects that dont use physics, having so many objects use
physics at once obviously murders your computer, im surprised i was able to run this at all(low settings)
4.in this kind of map it is also good to limit the amount of lights and other things that affect the environment.
5. detail is important so your environment wont look empty, but that does not mean you have to bump stuff into every corner of every room in your map. you must prioritize and put in the detail where its visible, fx. not under the staircase where its hidden.
and yes, I am sorry for not placing my images in those spoiler thingies, but i could not figure out how.