The limits are what the viewer applet can view with 640 MB of memory, and… the patience of your users. Because, if it worked correctly on my computer, I wouldn't expect my web users to wait more than 10 minutes to view a 3D model of a home, how amazing it would look like. Maybe, you could remove or replace the biggest 3D model; for example, just the Rhododendron occupies 1/4 of your .sh3d file!
Anyway, very nice house model [:)]