The Vive Pro in general (if operated with full resolution) does require a very good (high-end) graphics card. The GTX 1070 would be the minimum requirement, but, make sure that the resolution is actually set to anything below or at 100% as detailed in the "Best Practice" section here:
So in this case setting it 75% for example should already yield more performance. Or of course if it was set over 100%, then setting it 100% should also help.
I suppose that it was set over 100% which is why you were experiencing this low performance - please also definitely make sure that your graphics card drivers are fully up to date! Does that help?
Overall, it does boil down to the GPU mainly, so if you have around 8-16GB of RAM, then that is more than sufficient usually and it's recommended to focus on a good GPU.
Well now, my SteamVR Resolution was set (Recommended) to 150%. I put it down to 100%, and suddenly Ultra settings worked fine in VR. Such a simple thing. But will see how it goes. Thanks for that!