Found a free GPU monitoring app, called GPUZ.

Even with just the loft apartment loaded, GPUZ reported only 243MB of VRAM in use, so, yeah, the graphics card would've been a huge waist.

According to what little info I could find on how to boost performance in Poser's Preview Window, the only solution availble to try is to make sure OpenGL is selected as the preview engine, instead of SreeD, and it already is.

This is really annoying.