I never used OCCFD.
Right now there is a fast option available in MantiumWFlow MVRC edition. You will see soon. The mesh created there is about 1.5e6 cells large.
MantiumWFLow allows you to customize the simulations if you like. So you could make the cases faster if you want. I noticed that the main issue with coarsening up the case is that CoP gets shifted. So you have to find out how the fine and coarse results correlate. And as it is most likely vehicle specific that is your job.