300,000 polygons is enormous and completely unncessary for the scene that's pictured here. Bryce is quick to navigate because you're looking at a low-poly proxy, not your full scene. I'm not familiar with Truespace, but if its crawling, I'd assume that your poly count is the problem. Go on a polygon diet. The scene you've got above shouldn't be more than 50K polys, and it will both render and setup much faster.