Quinceañera party

I have recently discovered a new meaning to an old Spanish word. Michael Douglas, Sandy Kominsky in The Kominsky Method, says, explaining his personal relation to a shaky waiter: "I was MC at his granddaughter´s quinceañera party." Let´s look into it.
"Quinceañero," one who is fifteen. 15 in Spanish is also known as "la niña bonita" because all "quinceañeras" are supposed to be pretty, and just as number 22 is known as "two little ducks" in English and "los dos patitos in Spanish."
What I ignored was that "quinceañera" is a party in northern Mexico and other parts of HispanicAmerica, to celebrate the coming of age of young girls, otherwise known as "coming-out party," "sweet sixteen party" in the US or "puesta de largo" in days of old.
Spanish dictionaries do not mention this definition, but Merriam-Webster does, giving two spellings: "quinceañera" and "quinceanera."
Live and learn!