Yeah, not surprised. That GPU is roughly 15% of the performance of mine, which isn't even bleeding edge at this point. To put it in perspective, that card performs about 10% better than the one that came in my gaming laptop made in 2007. I wouldn't expect much even after optimizations. However, make sure you are plugged in and running in high performance mode, otherwise the game may be using your integrated graphics rather than the GPU.
I know it's an anaemic card, but it runs games like
War Thunder,
FFXIV: ARR,
Natural Selection 2,
Eve Online,
S.T.A.L.K.E.R: Clear Sky, etc. etc. tolerably well, and I would wager that they are all more demanding than
Original Sin, which to my eyes is just a few steps up from, say,
Path of Exile (which is easily max-able on my system).
