The 15 minute early thing compounds as well: each level of supervision expects their people to show 15min early for a variety of reasons; at the lowest levels it's to take roll and address absences ("send someone to go wake up Smith, NOW!") and to brief individual or small group* responsibilities abd/or meet up points, and might even include travel to an intermediary or ultimate rallying point which itself has a 15 minute early policy. And from there it continues. 15 minutes for each subgroup to arrive at and find their place in the bigger group, repeat until everyone is gathered. Could end up being hours early as an individual in order to account for this. In the end it's nothing really important and your day was "wasted" (cue separate discussion regarding "your" time in a military).
* group meaning a collection of people, not the occasionally-used military "Group"
* group meaning a collection of people, not the occasionally-used military "Group"