What is the difference between a sweet 16 and a qiuncieta

If you mean quinceañera then the first difference lies in age. A sweet sixteen is celebrated, quite obviously, on one's sixteenth birthday, while a quinceañera is celebrated on one's fifteenth birthday, as it is traditionally seen as the age a girl enters womanhood in Latinx culture. It began with the Aztecs who believed fifteen to be the age that boys became warriors and the age that girls became the mothers of future warriors. This is also significant because although modern quinceañeras may be rather extravagant similar to sweet sixteens, it was not intended to be that way originally.

This ties in with the biggest difference: culture. A sweet sixteen, as far as I know, can be celebrated by anyone of any culture, but a quinceañera is specifically a Latinx celebration, though it is celebrated in certain parts of Spain and Portugal as well.

Another difference is that a quinceañera is seen as comparable to debutante balls that were held in the United Kingdom and United States, which is again linked to the girl becoming a woman. 

Lastly, while it's not considered tradition everywhere, some choose to attend mass as part of the quinceañera celebration, while that wouldn't typically be associated with modern sweet sixteen parties.

Oofuv