You'll probably get a proper and better response if you ask in official Vray forum.
There are a lot of reasons that might increase render time. And i think it should take less than an hour for a complex scene for those specs (But i believe it can be reduced by adjusting settings & parameters. Often time people use those parameters excessively).
So it will be great if you can share some screenshots of scenes & their settings (+materials) etc.
I'm not sure but GPU acceleration doesn't necessarily speed it up if your GPU is worse than CPU which i think in your case is. (Or it might be because you're using a feature that is unsupported by GPUs yet)
Also take a look at ChaosGroup's benchmark. Use the search box for your specs. You can download standalone benchmark (top-right), test yours too and compare.