Just measured mine and also got 15.75 at the widest portion, which is actually across the lid.
The bottom slopes inward a bit; so including spigot, I got closer to 14.75 at base.
Enjoy the little things, for one day you may look back and realize they were the big things.
Primary: Citra Pale Ale
Kegged: Brown Ale, Porter, Sweet Stout, IPA, Amber