You're actually lean for some guy just keeping in shape! Most dont have a clue what their BF % is without a DEXA or underwater weighing. But really, so long as one is lean (which you are) and doesn't appear fat, it really doesn't matter, unless for curiosity's sake.
I think we can all just go by the mirror. If you look fat, you're fat. If you look lean, you're lean.
I think you're 15 - 17% perhaps. Who knows? Maybe a little lower.
Just for discussion's sake, I've noticed that many people, even with a good deal of exercise and not overeating cannot comfortably stay at some desired body fat percentages to appear very lean (not shredded though). They just can't sustain the amount of exercise or calorie restriction to appear very lean with taught skin year round. Even some competitors are like this. I myself, eating at a caloric level at which I am not over eating, and doing a good deal of exercise, likely stay at 15 to 17%. To maintain a lower percentage would require unsustainable practices.