Santa Cruz is one of the more expensive places to live in the US - you can expect to pay at least $600-900 in rent. $15k is about what you get if you TA, and that's barely enough to scrape by. Most folks wind up taking out loans on top of that - especially if you have kids or other expensive habits.
And I'm guessing that the average humanities stipend is $0. Most students at UCSC in the Social Science and Humanities aren't funded, and get their money from external sources or TAing.
Oh, just saw that this was asked 5 years ago - I'm sure you've figured that all out by now.