Why do Latino Christians treat their patron saint's day more importantly than their birthday? Would a fifteen-year-old girl's Quinceañera be as important as a birthday or more important than a birthday, with similar value to a patron saint's day or the day on which they would be confirmed in the church?
Not just Mexican, mostly a Catholic tradition. (http://www.catholic.org/saints/faq.php)
This is one way to carry-out this tradition: Catholics ask saints to give a word or two to God for them. So, if my name is Peter, I should IDENTIFY myself with Peter's Day, present gifts, ask people to help me with extra treatment/presents, so together with Saint Peter, in God's favor, I can ask what I want/need. Can't get that on a b-day.
So, it is a TOOL to help a Catholic identify with God. Never the less, a tradition, not that is right or wrong. But far from the truth.
Quinceañera, is a right-of-passage, personal birthday. Not answered here.