Sisters (Pleiades) - Constellation
Sisters (North London)
Dials (Brighton)
Tiles (game in India played by two teams, using a ball and a stack of 7 tiles)
Colours of a rainbow (it is a continuum really)
Names of musical notes
Wonders of the World (ancient and modern)
Days of the week
Seven swans a swimming
Soda comes in groups of 6
states
dogs
what comes in groups of 12
Arms, legs.
Inches in a foot
gaggle of geese
In mathematics, a group of 15 items is known as a quindecad. Some common items that come in groups of 15 include eggs in a carton, months in a quarter, and players on a rugby team. Additionally, elements in the lanthanide series of the periodic table have atomic numbers that are multiples of 15.
Case of beer
Pennies
scorpion legs