You're still missing the point. The biggest advantage of YC is advice and connections. (Actually, I suspect an even bigger advantage is a supportive peer group and a sense that you don't want to let your investors down, but nobody's mentioned that yet.) That's worth a lot more than a bank loan, because it's a lot more than money. A bank loan for $15,000 will not increase your startup's chances of success nearly as much as being accepted to YC.