Slow GPU rendering

I just opened up a project to make a render, but its going extremely slow. i usually render this specific object in under 20 minutes, but now its taking forever.

3.7M tris and i even went down from level 3 subsurf to level 1 and 1500 samples to 500.

im using two GTX 970s, SLI is disabled, GPU compute is selected in the render panel, (2x)GTX970 is selected in my CUDA preferences, GPUs are at 99-100% usage and the samples are 512x512.

any clues why it renders at gameboy speeds now?

I’m not sure what we are supposed to say without more information…

If that very scene rendered much faster before, well, what did you change, then?
Be it with your machine (Drivers? OS updates?), Blender (New version?) or the scene (Render settings?) - something must have been changed.

But unfortunately nobody else than you will be able to say what…