To do this, you would need to create another PI Tag Attribute to store the trigger condition 15 minutes before the real time trigger.
For example, you could have a trigger condition that follows the logic: Trigger if the tag "Sinusoid" is less than 50:
You would create an analysis with this trigger condition. Then use advanced options to store the value 15min before the trigger time:
You can then store this analysis into a tag (TagA). Then use TagA to trigger the event frame.
The only caveat would be that this would also cause the event frame to close 15min earlier. You can get around this with a creative EndTrigger condition.
Really good idea. Finally I did it changing the start and end conditions, but I will take this for a future use.