Judging optical quality in anything other than field conditions is folly.
Regarding 15s, and tripod-based 'hunting' in general, the truly wonderful thing they do for you is yield a whole new world of outdoor experience. You will find yourself making special trips out all year long just to glass and see what's up. And you will discover a world that you only stumble through otherwise. In that way it's a lot like treestand hunting -- all sorts of bio plays out in front of you, and at close range.
With 15s, close range takes on whole new meaning. It's a little like learning archery in order to extend the hunting season, except better. Which is why I vote to get any good glass and sally forth.
