does anyone know, is it possible to run shadow warrior 2 with only 6gb of ram?
i don't have the required 8gb...

You can run most things with less ram thanks to virtual memory but the experience can vary from horrible to just fine.
To comparec, 1600mhz ddr3 memory got read/write speeds around 8500mb/s while a good mechanical hdd(which will be used for virtual ram) will hit 200mb/s. A ssd would of course make things smoother but still not even comparable to ram speeds.

Not sure how gog refunds really work so I'd just download a demo and see how it performed.

I'm running it on my system with 4GB DDR2.
The game uses about 2.3GB for me, so I think you should be fine.