Don't have pro, but can i use somthing like occlusion culling?

There are some occlusion culling products on the asset store, including InstantOC and my own product, SECTR VIS. Before you buy something, though, you should make sure you know that rendering is actually your problem. Without Pro you don't have a profiler, but try doing things like rendering to a really small res screen vs not rendering at all vs rendering but disabling AI or physics. Once you find the thing that's slowest, you'll know where you actually need to optimize. Whatever you do, don't just assume that a certain thing is slow as it is often something else.