I agree it's a good idea to get something going while still employed. I disagree it's "foolish" not to though. I think the #1 cause of failure for most startups is never taking a plunge at any point. I know too many people who have dreams that remain dreams for so long they're eventually forgotten. It can be
really hard to do a good job on a side project if you're the kind of person who tends work really intensely on one thing at a time.
Better to take the risk (if you can) and have a real shot at success than always be waiting until "tomorrow". He's forcing himself to succeed or fail. People are capable of a lot when they don't have an easy out. How many successful companies were side projects? Maybe 5-10%? That's a damn low number if you realize how many people have side projects they wish they had the balls to turn into companies.
My big concern is that $15k just isn't that much cash. Unless you're living somewhere ridiculously cheap or rent free (parents) that's probably just a few months. Not enough to get the profitability for almost anyone. YC companies only work because they get 3-4 months free, can spend their own money after that, and have a really good shot at getting funding.
Hats off to you, Palish. Good luck.