Yep, as previously mentioned, honey is an invert sugar and highly fermentable. The trick is to pick the right yeast and to give it enough nutrients to get to that high an alcohol content. It's not easy.
Best bet for yeast would be ec-1118, which can tolerate up to 18%ABV. Very easy to use, and it's a beast. Or go with WLP-099, which can go to 25%ABV, if you treat it right. But she's a finicky yeast, and you need to treat her right.
In both cases, you'll want to use a lot of yeast nutrient, and add it in batches. Commonly you use 1/3 of the total amount at first, then the next 1/3 after a few days, and then the last 1/3 when the yeast are slowing down.
To hit that high an alcohol content, you'll need to step feed your mead. So if you expect it to be 3#/gallon, start with 2#/gallon and add the extra honey as fermentation slows. You need to acclimate the yeast to a high alcohol environment, so add some of the honey, then add some more, then add some more until you're at your final alcohol level. Does that make sense?