In my experience, whenever I’ve had any problems with performance of collisions, it’s generally because my collision solids are attempting to collide with far more than I thought they were.
How simple is your floor terrain? Dozens of polygons? Or thousands? Thousands of polygons look nice for rendering, but you really only want to collide with dozens. If you haven’t done it already, you may need to have a reduced-complexity version of your floor for the purposes of collisions.
Also, the showCollisions() step is useful for lighting up the polygons that it’s testing against. Make sure that it’s only a handful.
David