How many servings in a keg?
Not taking into account head space (the foam on top of each glass, or what Jac McTighe calls “profit”) or spillage, all you have to do is run the math: 15.5 gallons = 1,984 ounces = 124 pints, or 135 12oz. servings. For planning purposes, I’d figure on 120 servings per keg. As to how many people that serves, it depends on how thirsty your friends are.