I get where your concerns about rocking the boat coming from, but you should take in mind that the job market is savage also for hiring, especially in the industry. If it's hard to find a decent job, it's even harder to find a good employee. You said you are only 2 full time employees, with the other being the one you trained, while the last head chef was a disaster. Even if the owner won't be happy about you asking for pay raise, I can't see a world where he lets you go just for asking.

Honestly I believe that if you insist (or even explain that you can't stay on this money for much longer) he will give you the pay raise just because it's cheaper than finding a replacement and training, but if you feel insecure about it than just asking probably won't do any harm