Having tested this numerous times, I can tell you..too many colliders is a problem. Speedtrees work MUCH better if you take out the colliders as do 3dForge houses, which I have tested numerous times. A tiny village or a house in the wilderness...maybe not a problem. But a city with multi-level houses, props, etc, have many colliders. Combining some of them really helps. That works with 3dForge, if you have a tool that combines colliders as well as meshes. But it is easy enough to add a collider to the house after you build it. With Octave3d, I cannot select the house outside of using Octave3d and add a new collider. I have to move the items outside of Octave3d's World Object. Selecting and turning to prefabs might work. I would then move it outside of his world object and add the collider. I am going to try that now. Well..not now as I am writing a design doc for my programmer to use at the moment..but later.