Quarter-hourly

With the utmost precaution we crept upon the summit, and down the breast-work towards the onter edge of the rampart, when the sentinel made his quarter-hourly cry of “Sentinelle, prenez garde à vous,” similar to our “All's well"

Source: wiktionary

For example, currently, smart meters can be configured to generate hourly, half-hourly, or quarter-hourly readings

Source: wiktionary

We can furnish Bells, Tubes or Tongs, which can be attached to any Clock, arranged to strike quarter hourly the Westminster or Whittington Chimes

Source: wiktionary

Only upon this quiet there broke quarter-hourly the chimes of the Church of the Sorbonne, completing, at the hour, a bar of music.

Source: wiktionary