15FPS assuming you are playing in the exterior view?
I run a nVIDIA GeForce GT 525M on my L502X model Dell with OpenBVE.
Whilst using the R46, I get 90-100FPS while running in Cab mode and about 40-60 running exterior mode.
I don't have MSI Afterburner, but I can tell you that I had various chrome tabs open, iTunes open, Steam, CS:GO and Ventrilo on at the same time OpenBVE was operating and the FPS didn't really fluctuate.