From Longman Dictionary of Contemporary Englishfifteenfif‧teen /ˌfɪfˈtiːn◂/ ●●● S3 W3 number, noun 1 HMNthe number 15 a coastal village fifteen miles south of Tourane They met when she was fifteen (=15 years old).2 [countable] a team of 15 players in Rugby Union —fifteenth adjective, pronoun in the fifteenth century her fifteenth birthday I’m planning to leave on the fifteenth (=the 15th day of the month).
Examples from the Corpus
the fifteenth• Let's have dinner on the fifteenth.Origin fifteen Old English fiftene, from fif “five” + tien “ten” 