general_fact: 15508 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 15508 is an uninteresting number.
trivia: 15508 is an unremarkable number.
historical_date: June 16th is the day in 1972 that the largest single-site hydro-electric power project in Canada is inaugurated at Churchill Falls, Labrador.