What kind of support does a 15 inch overhang on an island require?

[Warpy]

3. The corbels wiil be decorative

but if they're wood instead of plastic, they'll add considerable stability. You won't have to freak out when people are resting their heads in their hands with their elbows on it.

I had one in my trailer that was held up with wooden angle braces, about 42 inches long and only three braces, topped with Formica, and that thing felt rickety although it wasn't. I didn't ask it to do much, though.