Why do Latino Christians treat their patron saint's day more importantly than their birthday? 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.