The very first you could do is remove the rims and wheels (you can later import the rims separately). Keep the suspension, because you'll need to map it later. After that, you could try these two methods in Blender to lower the points and triangles.
Method 1 (un-subdivide) :
https://www.youtube.com/watch?v=BATG3b1ZFG4
Method 2 (decimate) :
https://www.youtube.com/watch?v=GrD71-wXrIA
Overall, you could try to find the most detailed parts and recreate them. Sometimes dashboards, rims, tires, steering wheels, and small details like that have the most vertices. You could check if there are invisible parts inside the vehicle, which nobody will see. You can delete them as well.