You can reduce your texture quality to LOW, keep your FPM levels small and compact, and focus on multiple levels for your game, keep CSG activity to a minimum by using fewer doors and windows and keep character and other high polygon entities to a minimum. As you test, make mental notes about which additions cause a longer waiting time and then avoid or curtail such additions. We also have ideas at this end how we can speed up the build process for all users (such as when the map does not change, re-use the last universe geometry, etc).
"We are the knights who say...eki eki eki fatang loopzoing, zanziga....ni"