Collisions optimization

Hello,

I tried to use the UCX collision because I needed precise collisions.
I a rock model and I scale it sometimes in my game up to 10x, so when a player walks on it, you can see the player flying over the little holes of the rock (http://puu.sh/agBHT/c5570f8b7b.jpg)

So in my 3D software I duplicated my mesh and named it UCX_MeshName.
It worked, but the problem is that the collision primitives is now to 940.
There was before that only 24…
Is that a huge optimization killer?
My mesh is quite complex and I really need the player not to fly over…

Thanks!