general_fact: 15 is the approximate speed in miles per hour a penguin swims at.
math_fact: 15 is a triangular number, a hexagonal number, a pentatope number and the 4th Bell number.
trivia: 15 is the number of balls in the eight ball variant of billiards.
historical_date: January 15th is the day in 1991 that the United Nations deadline for the withdrawal of Iraqi forces from occupied Kuwait expires, preparing the way for the start of Operation Desert Storm.