20 minutes to open that? I think your opening that in a Model window, which would do a poly to spline conversion (and take 20 minutes), instead of opening it in a Choreography window as Prop, which would treat it just like a poly model (and be fast).
If you thought you were forced to open it in a Model window because you needed to add the wheels separate, then what you should do is create a rig that consists of "chasis," "tire1," "tire2,"... then constraint the Props to the appropriate Bones.
If you are opening this as a Prop, and it takes 20 minutes, then file an Error Report, son.
Interesting experimentation.