A gallon in the USA is 6 pints but in the UK it is 8 pints. Therefore, one third of a gallon in the US is 2 pints, but in the UK it is 2 and 2/3 pints.

One quart is equal to a quarter of a gallon. One gallon is equal to eight pints, therefore one quarter of a gallon is two pints. 15 pints is equal to 15 / 2 = 7.5 quarts.