Grainy output from ProRender

I’m getting very grainy renders from ProRender and when trying to use the new PBR materials.
The standard render engine is also producing very grainy renders.
Could this be caused by an incompatible graphics card driver?
- Quadro K620
- driver ver: 391.74 (newest)

attachments: material with grainy sample sphere
proRender sample
standard render sample

I’ve tried area lights and omni lights. both seem to make grainy surfaces when I use multiple reflection layers in the material.