No there is no demo. Steam does have a refund policy, though.
Do you know anyone locally who has the game, or might be interested in getting it, who could try it on your laptop?
Did the other user say they were using a similar video card? The Passmark benchmark for your video card is 2/3 of the listed minimum, but at a reasonable resolution I wouldn't be surprised if it gave acceptable performance. I have not seen any feedback on below-spec results for D:OS 2 yet, though.
