In theory it will depend on card tier and performance target. It could be much more for high refresh rates. Remember the 2080 Ti takes 1.5ms for 4k DLSS to run and the 2060 takes 2.5ms, and we can probably assume* similar runtimes for similarly fast Ampere cards. At 60 fps (16ms frametime) that's indeed less than 10% on the 2080 Ti, but 15% for the 2060. If targeting 144Hz (7ms frametime) on the other hand it's 21% and 35% increase respectively.
* The tensor flops with sparsity increase from Turing is equal to FMA increase, 2x per SM. Neither are likely to reach the 2x performance in practice, the assumtion being that the per SM performance gain will be similar both for rasterisation and DLSS.