15 lbs is possible for that fish. I enlarged the picture, and based on the length of his pinkie from the middle knuckle to the tip of the pinkie that fish is 14 pinkies long. My pinkie is about 2 inches long.
So that fish could have been 28" long. I contacted a local big bass expert and he says a 26"-28" long bass is about 15+ lbs.
I've gotta get a life huh?