Considering I tested Vegas Pro 15 Trial on my 970m laptop. It was slow to render anything. I don’t think there’s great support in OpenCL for Nvidia. I have an AMD 7570M laptop to compare, and in comparison to the 970M it should be lower-end but rendering times with that GPU was remarkably quicker.
From experience with Pro 10 on my old desktop, that rendered quickly too with the 560Ti. You say 960M, yes? Which laptop is it?