Another thing that would help would be to replace a few surfaces to simplify them - for example if you use edit > Separate on the "side wall" pieces of the voronoi part and turn on control points for them you'll see that although it's a planar surface it's not just a simple large plane, it's made up of a lot of points that wind around. If you delete those and then replace them with simple planes (open up a planar hole and then select the part and run Construct > Planar) that might also help.

- Michael