I know this is kind of an old post, but to answer your question directly about how to reduce the size of the build data there are quite a few things you can do. Try tweaking some of the parameters in your lighting. For instance, if you have a sky light try reducing the intensity of it. I built a game that had a total of 105 levels… using direct light as the main lighting source and a sky light to give it that nice, lush lighting volume my total build data was roughly 15GB for all the levels, and they were small levels. I got rid of the sky light and added a secondary direct light, reduced the intensity of both direct light sources, turned shadows off on one of them, and set the light to shine opposite of the first light source. This knocked 10 GB off of my total build size. Sure, it doesn’t have that super nice looking glow effect, but it really optimized my game overall.