IMHO - I would just get a low cost 10 HP VFD (under $200)
I am not a machinist, but it seems to me that the only time you would need 15 HP is when you are making a heavy cut on a large work piece.
The 10 HP VFD will run the motor just fine.
It will simply trip off line if the load ever exceeds the VFD capacity.
Go for it