Collisions have a huge impact on performance, and usually processing of collisions are left up to the collision events rather than being ignored at the server.
Currently you can only filter out a single name or ID key - you cannot exclude other types. Add:
llCollisionTypeFilter(integer type, integer status)
where type=AGENT,SCRIPTED,ACTIVE and status=TRUE/FALSE
Also independent of llMinEventDelay() please add:
llCollisionEventRate(float rate)
would also help cut down high rate collisions.