The pz3 size is quite small, but not an indication of the problem
I'd be looking at my render settings, ie. max texture size, samples etc.
I'd also completely turn off my pc and restart afresh before trying to render again.
The sad thing is that having a large texture size setting really makes a big difference to the quality of a render (in close-ups), but chews up your RAM.
I actually love P6 - miles better than P5 and far less buggy than P7.