Quickbase Notifications

No problem,
Make a new date time field on your record called [Date /Time to trigger email]
Set the notification  to instead trigger in that field.

Make a Pipeline to trigger in the same condition that your old notification was firing on.

The second step of the pipeline will be from the Clock Channel and it will be a Pause Step.  Enter 15m as the amount of time to wait.  The step has built in help for other time period syntaxes.

then the next step will be to update the trigger record in the A and update the field [Date /Time to trigger email] with the value
{{ time.now }}

That will trigger the Notification.