I don't meant to put a crimp on your day, but you do understand that for the money you pay for a pre-built system, you can probably build a more powerful one yourself for the same price 99 times out of 100?
+1,000 For the price of that i5 machine, you could just build your own much more powerful system (like mine, for example. My system cost me a little over $900, and that was a while back now. That didn't include a case or monitor, but still).
And I can't find ANY info on the GT615 even existing, except for in those Lenovo systems, but my guess is that it's a re-badge of a very low end 500 series card (or even worse).