What happens when you choose to ignore or close the prompt saying low memory? Does it continue to play as normal or does it put you in windowed mode? I get this sometimes with Crisis2 and I just ignore it and game still plays fine. Windows should automatically free up resources need for main program you using at the moment.That was a 256 8gb....not sure if that compares exactly. Turned on high performance and still got the error...kinda irritating. Anyone able to tell me if their physical memory shows the same with nothing open per my pics. 128 4 gb version.
Its likely something simple as your device should have no issue, even at 4gb ram, of running Diablo 3.