Mesh is mesh. It all gets converted to poly when rendered out. Using render layers is just the de facto way it's done for large scenes. If you can't do that, the only thing I can suggest is go into render globals and make sure you're using a small low quality render until you get the render view to be exactly the way you want. Then, up it to high quality and be patient. The only other way is really to rebuild your surfaces so that they're less dense.