I picked up the 15 as my first tweener, after having bought a BK-2 and BK-9, in that order. You can't NOT have a BK-9! I went to the trouble of stripping it, and then taking the blade secondary grind to a pretty high polish. My intent was to then patina it, but after I finished, I liked the polish so much, I left it. Then I decided it was too pretty to use. It has been hiding in my closet ever since. I honestly don't think that blade has cut anything, and is actually my first and only safe queen, out of knives that cost up to 5 times as much. Not sure what my problem it, but it just doesn't work for me, doesn't speak to me (not unlike the BK-10, but that is another story). I think I'm going to re-appropriate it to the kitchen, it needs to be used, and it would make a great barbeque knife. Anyway....
I just took delivery of a BK-17, after having bought a BK-11 subsequent to the 15. I think the 17 will fit my preferences and usage much better than the 15 or the 16. If not, I'll buy a 16, someday after the DoD Furloughs are over.