What are your hardware specs? FM7 conversions are notorious resource hogs and very time consuming to optimise, but 20fps while hot-lapping seems incredibly low.
I can daytime race against ~8 low-poly cars at Maple Valley in VR at 45ASW (stock 980ti/6600k) but struggle to hot-lap without significant slowdown at Rio, Prague, and Lime Rock. Maple Valley is currently somewhere between these tracks and the more optimised FM7 tracks (Alps, Bathurst, Fujimi Kaido) for me. Better optimisation may come at Maple Valley if somebody wants to take it on.
What sort of performance are others getting at MV (and are you racing in 2D/VR, and what are your specs and race parameters)?