I opened the STP file and sliced out two roller teeth on the gear shaft to show you the kind of work that can be put into the geometry to simplify it.
On the left is the original tooth, meshed with default parameters. It has 5727 nodes and 3110 elements. The simplified tooth on the right has 2114 nodes, so less than half the nodes and only 1064 elements, or about 1/3 of the elements.
Another advantage of simplified geometry, the element quality improves. The minimum element quality in the original tooth was down to 0.14, but the minimum element quality in the simplified tooth went up to 0.31, about twice as good.
You can do this kind of improvement over the entire model and get down to a mode that might run.