Is the improvement as big as haswell over sandy bridge or not?
Ivy to Haswell was about 30% better, but Haswell to Skylake is closer to 5-10%
I would say more like 15-25%. Anandtech showed a 17.9% increase on the official benchmark and that was with fairly slow ram. It's not as much of a jump as haswell (30%~) or sandy bridge (40%~) was but it's a lot more than ivy bridge (5%~).