It's the lights that will kill the render time. I am assuming theya re radial lights you are using, and if this is the case you can get along with less of them. Delete some of them (more than 10) that are not specifically lighting a certain area, and then make 3 new ones. Spread them around the scene so they are high up and next to the edges. Make falloff none, and make the intensity 2 for two of the lights, and 1 for the other one. There! You just save yourself at least ten lights! Tip: you don't need to do soft shadows...simply turn the intensity of shadows in the sky lab down to 25 or so.