The 1500 has the slower core frequency, but Nvidia did something funky here, gaming graphics cards with the same core run higher core frequencies. Maybe it's been downclocked for stability or power consumption reasons?
The 1500 has higher memory frequency and bandwidth.
I would probably chose the 1500, as it may be a bit more stable.
But then again, there could be almost no difference.
Perhaps you could use something like RivaTuner to crank the core frequency up a bit on this card?