A traditional quinceañera vals is a waltz.
The word vals is the Spanish form of waltz, the partnered dance traditionally performed in triple meter. In a formal quinceañera, the celebrant may dance with her father, relatives, or members of her court. The dance can be slow and ceremonial, or it can be arranged as a more elaborate choreographed performance.
The waltz became an important part of formal social dancing in Europe and later spread widely through the Americas. Quinceañera celebrations adapted that ballroom tradition to a family-centered rite of passage. The dance’s formal style helps mark the event as different from an ordinary birthday party.
A quinceañera may include many other musical styles, including regional Mexican music, salsa, cumbia, bachata, and contemporary pop. Those additions do not change the meaning of vals. The traditional vals is specifically the waltz portion, even when a modern performance blends ballroom steps with other choreography.