Does the word quinceañera need to be capitalized?

The term quinceañera does not necessarily need to be capitalized. A quinceañera is a coming-of-age celebration in honor of a girl's fifteenth birthday. Traditionally in many Latin American cultures, a young woman was considered eligible to be married at the age of fifteen. Today, most quinceañera celebrations do not have the expectation that the girl will become married soon after. Instead, it is a celebration of ethnic identity and of the young woman's growing responsibilities and role as an adult.

While the quinceañera is a holiday or celebration, you don't need to capitalize it like you might do with the words Christmas or Independence Day. If it helps,  you can think of the term as another way to say, "fifteenth birthday." In English we don't capitalize the word birthday unless we are referring to an official title or it comes at the beginning of a sentence. A good rule of thumb is that if you feel you would capitalize the word birthday in a sentence,  you could capitalize quinceañera just the same.