This question can't be answered without knowing the current time. To determine what time it was 15 hours ago, simply subtract 15 hours from the current time. For example:
- If it's currently 3 PM: 15 hours ago it was 12 AM (midnight).
- If it's currently 8 AM: 15 hours ago it was 7 PM the previous day.
You can easily calculate this using a clock, a calendar application on your computer or phone, or an online time calculator.
