Don't worry so much about polygon counts unless you are also using the models in a game engine or realtime renderer (or just use two sets of models).  While doing this project, I noticed that geometry had much less to do with render times than the number and size of textures used and how much of the image used transparency.  The slowest part of the scene to render is the window, as Poser has to combine the reflectivity of the window surface with the background through the (not fully) transparent window.