The operations team wants to track website activity in 15-minute intervals rather than by individual event timestamps.
The events table contains event_ts for each recorded action. Each event belongs to the quarter-hour interval in which it occurred, beginning at HH:00, HH:15, HH:30, or HH:45. For example, an event at 10:10 belongs to the 10:00 interval, while one at 10:45 belongs to the 10:45 interval.
Prepare a summary showing the number of events in each interval containing at least one event. For consistent output, show bucket_start as text formatted YYYY-MM-DD HH:MM:SS.
Ordering: Sort by bucket_start in ascending order.