If we're comparing free food to basic income, the comparison should be against basic income that's just enough to feed yourself. Somewhere around $1000/person.

Even if you want full basic income, I'd argue that $15,000 is high. As a (Canadian) student in an expensive city my living expenses (everything but tuition) are easily under $10,000 USD. Using the numbers you linked we're almost certainly talking about less than $8,000/person to keep everyone above the poverty line (the exact number depends on what the average family unit looks like, which I don't know).

(All numbers per year)