Go get the free tree from X frog.It's 350,000 polys but it's nice. they got a few good trees there in samples somewhere that are nice. you got to look around a bit to find them. Use ambient 100 % objects for the lights then maybe you'll only need 1 or two real lights and don't use spheres for objects to hang from the tree use cubes and piramids maybe go grab my not so primitive free set and find a few cool ones there. There way less polys than spheres. Group and group some more !