The old ABC FM network fed news at :15.Different stations did news at different times. The Bill Drake RKO stations were famous for news at :20 before the hour (and in the early days, both :20 after and :20 before). Some stations went for news at :15 and :45.
KIOA in Des Moines did news at :15 and :45; WHB in Kansas City did it at :55 and :20.
On a different scale, the radio station in my mother's hometown in Missouri does local news at :15. It always has, ever since its first day on the air in 1955. I don't know why. In recent years, it's been running network news (first AP, more recently, "Fox") at the top of the hour and a statewide network newscast right after that. A good part of the day on that station is still live.