Ahhh. So you used a wrapper or a library? Interesting then. I had assumed that almost every rendering method enables frustrum, occlusion, and backface culling by default if only to clear the number of objects needed to be tracked in memory. One thing I noticed in your game is that it's based on the absolute mouse position, which with a 16:9 window makes it difficult to turn in certain situations because your horizontal movement space is much larger than the vertical movement space and that adversely affects turning speed. Changing so that is based just on horizontal mouse movement or adding keyboard controls might be better.