I've done a couple of ISO comparisons above. At ISO 200 and 3200. As you can see they are pretty similar and since both sensors are made by Sony that's not really a surprise. The a6000 has a higher pixel density so it does show just how good that 24MP sensor is. However there is one thing worth pointing out. The Sony examples were with the Sony / Zeiss 55mm f.1,8 lens and the Leica examples with the 18-55mm zoom.
As you can see the sharpness is the same. And that's because the Leica zoom is very very good. Which of course you'd expect given it's cost. But just imagine if I did this comparison with the Sony 18-55mm or 16-50mm. You certainly wouldn't see the same results then. I would also point out that the Leica zoom was wide open and the Sony / Zeiss prime stopped down to f/4.
But both cameras are excellent when it comes to image quality at all ISO's and to split hairs doesn't really achieve anything. With decent lenses on both you get top class results. Nuff said.