One way to speed up the render time is to render your background and foreground separately in two images. For the background render just hide the foreground figure(s). For the foreground, render over black and export as a .tif or .psd file so you have an alpha channel. You can then composite the images in PSP or PS. The alpha channel will make the black background in the foreground image transparent so the rendered background shows. Any changes you may need to make in the foreground will render quicker since your using a smaller area. I do most of my backgrounds in PS then use this process to overlay the Poser figures.