It would be cool to also get notified shortly before the workshop starts because 15 minutes is a long time span and I already forgot the workshop a few times because it was 15 minutes before.
To fix that, it would be great to get notified 5 or less minutes before as well so you can actually join the meeting.
The simplest approach would be to call the azure function WakeupTimerCallback not only 15 minutes but also 5 or less minutes before a workshop starts.