Hi,
Thanks for your swift reply. I've been double checking it with our main developers and because of several reasons, supported V-Ray versions are now in the FP6 identical to the RC plug-in > V-Ray and V-Ray RT supported versions are 2.5 or greater for V-Ray 2, and 3.3 or greater for V-Ray 3. Upgrading the V-Ray to a newer version would be highly recommendable. As far as I know, if you're already using any of the V-Ray 3.x version upgradings to another 3.x version should be free of charge and there are significant speed improvements.
Best regards,