15 Gallon Tank?

Anybody know if it is possible a '74 Duster came with a 15 gallon tank? I thought my car was having some sort of issue, because the gas gauge dropped pretty quick and fill ups were too frequent. MPG is OK averaging 14, which is good for the 340 the way I drive it, using the 3rd and 4th barrels quite often. Seemed like it never took more than about 10-12 gallons at the gas station. So yesterday I put a can in the trunk and ran it until it quit. Fill up then only took 15 gallons.

Tks...