It's about eleven times as big as a Bowling Ball
In other words, 15.50 gallons is 11.1349501890 times the size of a Bowling Ball, and the size of a Bowling Ball is 0.089807316874 times that amount.(USBC specifications; tenpin)
According to United States Bowling Congress specifications, a tenpin bowling ball should measure at least 10.795 cm (4.25 in) in radius for a total volume of about 1.39201341150 gallons. Because regulation balls measure the same diameter irrespective of their weight, ball density varies by size and balls weighing less than about 5 kg (11 lbs) will float in water.
It's about one-tenth as big as a Hot Tub
In other words, 15.50 gallons is 0.0816 times the size of a Hot Tub, and the size of a Hot Tub is 12.30 times that amount.(for Lifesmart Rock Solid Simplicity Plug and Play 4 Person Spa With 12 Jets) (a.k.a. Spa, a.k.a. Jacuzzi, a.k.a. Whirlpool) (Advertised Capacity)
An average, four-person hot tub holds 190 gallons of water. Modern hot tubs became popular outside of Japan starting in about 1940.
It's about thirty times as big as a Human Stomach
It's about forty times as big as an Ostrich Egg
In other words, 15.50 gallons is 35.950 times the size of an Ostrich Egg, and the size of an Ostrich Egg is 0.02782 times that amount.(Struthio camelus) (for common ostrich; average)
The largest egg produced by living birds, ostrich eggs measure about 0.42270 gallons in volume. The eggs take about nine weeks to hatch, with males and females taking turns incubating them.
It's about 100 times as big as a STARBUCKS Venti Coffee
In other words, 15.50 gallons is 99 times the size of a STARBUCKS Venti Coffee, and the size of a STARBUCKS Venti Coffee is 0.01 times that amount.A STARBUCKS Venti coffee drink measures 0.160 gallons. The name of the size, Venti, is the Italian word for twenty.
It's about 100 times as big as a Blood Donation
It's about 200 times as big as a Baseball (packed)
In other words, 15.50 gallons is 178.497280 times the size of a Baseball (packed), and the size of a Baseball (packed) is 0.0056023263 times that amount.(64% packing density) (MLB rules)
Per Major League Baseball rules, a baseball must measure between about 0.053292311 gallons and 0.057857841 gallons. A major league pitcher can throw a fastball at up to 150 kph (91 mph).