Maybe he forgot, or it was just a mistake the author made.
15
Currently CARICOM has 15 full members, 5 associate members and 7 observers.
The United Nations Security Council has 15 members.
In 2013 they are from the ages 15-18 Who is 15 in the group
15
15
15
The one where the highest and lowest members differ by 15.
Rugby Union.
15
Increasing from 15 to 27 members