Help Rufus's friend

Fellow beekeeper, Rufus has a friend, OG, who is struggling to find 15 facts about the number 15 for a design project. At the risk of being a bee bore, I have suggested:

• As soon as 15 or more honeybees indicate the same new nest site for a swarm, the colony prepares to move.
• A queen bee has a retinue of about 15 (alternating) honeybees.
• Honeybees cruise at about 15mph.
• 15 stings in one day is enough to make me burst into floods of tears.

I'm sure you can do better.