Yep, for the round rock you can use a static Sphere geom (with no body).
I don't know of any memory leaks etc so I'm not sure why you get those slowdowns. Of course there could be a million and one reasons, but I would double check that you're destroying not only the body/geoms but also any joints that are holding them together. Destroy any unused spaces. As a test you could reposition (re-use) the body/geoms to see if that cures the problem, it may help find the cause. Also check for straying geoms that may have been created beneath the TriMeshes etc as that would probably cause instability or slowdowns. If you're creating static rocks that are in contact with the TriMeshes, make sure they're in the same sub-space with internal space collide mode disabled.
Let me know if you need anymore info ;)
I don't know of any memory leaks etc so I'm not sure why you get those slowdowns. Of course there could be a million and one reasons, but I would double check that you're destroying not only the body/geoms but also any joints that are holding them together. Destroy any unused spaces. As a test you could reposition (re-use) the body/geoms to see if that cures the problem, it may help find the cause. Also check for straying geoms that may have been created beneath the TriMeshes etc as that would probably cause instability or slowdowns. If you're creating static rocks that are in contact with the TriMeshes, make sure they're in the same sub-space with internal space collide mode disabled.
Let me know if you need anymore info ;)