I re-installed Rhino 5 (SR12) and V ray (1.5) on my computer after updating to a new hard drive and graphics card, however, the VRAY User Interface has an extremely slow response time. This is for all components of Vray (Material Editor, Options, Frame Buffer)
Graphics Card: NVIDIA Quadro 4000
Rhino 5 64bit (Windows)
Vrfay 1.5 64bit
I’d check your Windows updates and make sure you have everything up to date and successfully installed from Microsoft. Also check this page regarding using Quadro cards. You might need to adjust some performance settings or use an alternate driver. http://wiki.mcneel.com/rhino/nvidiainfo
These are both guesses based on your description so I’d suggest asking the Vray developers too on the Vray support forum.