The optimal solution is to have the slowest people crossing together; here is the order:
1. The two sober guys climb up first = 2 minutes
2. The “decade recovery dude” climbs back down = 3 minutes
3. Next, the two tipsy guys crawl up = 13 minutes
4. The “other recovery dude” comes back down = 15 minutes
5. Two recovery guys share bits of wisdom as they climb up together again = 17 minutes, just in time to make the meeting!