There are Sweet-16s and there are Quinceaneras, and while there are a lot of simularities, there are also some differences.
Primarily, when we're talking about Quinceaneras for ethnic Mexicans, we're not necessarily talking about the purely indulgent events that the Sweet 16 is and that the Quinceanera is for other Hispanic groups.
For Mexicans, yes, it's kind of an indulgence, but it's also a lot more of a "you gotta do it" event...like wedding receptions. Thus, you will see ethnic Mexican families of all economic levels scrimping and saving as necessary to make it happen...and they do take the photography seriously (more seriously than other groups take wedding photography). They may scimp on other areas to get good photography.
So it's necesssary to take it seriously even at the lesser income levels, because if they're doing it at all, they're taking the photography very seriously themselves.
To that extent, it can be very satisfying. It's good when people take what you do seriously.
I've done one of them, but the market in my area is still maturing (literally...I'm doing a good number of Confirmations right now). If I were based in Texas, I'd make them a priority of my business.