For 6 gallons pre-boil, yes.
Boil vigor and batch size also matter a lot. Most people I know boiloff at about 15% per hour for 5- or 6-gallon batches with a strong vigorous boil. However some will go as low as 8-10%.
Meanwhile, I'm a small batch guy of just ~2-gallon batches and my boiloff is around 28% most of the time, although recently I've been playing around with a slow simmer vs. the hard rolling boil that I always did in the past, so perhaps I can get that down into the 10-15% range with a slow simmer. I probably should be doing that to emulate more closely what commercial breweries are doing, which is around 5-8% if memory serves.