Here's the thing: Your brother is fighting against two liberal policies--forcing employers to pay someone more than they're worth and permissive policies with illegal aliens.
If you've got to pay someone $15 an hour--even if they aren't worth that, the employer is going to find another solution if possible--like McDonald's new kiosks. More on that later. Let's not forget that $15 an hour isn't $15 an hour. Because the employer also has to chip in half to FICA and Social Security and pay workman's comp insurance. On top of that is the Obamacare health insurance mandate and pretty soon your $15 an hour employee is costing more like $30 or 45 an hour.
On the other hand, if Pablo will wash dishes for $5 an hour cash, well, the math is simple. Even with a risk of fines. And with a government that is turning loose violent drug felons, and declining to prosecute for serious crimes, is that really a big risk?
I mention dishwashing because that was my first job. Interestingly, the second dishwashing job I took, the boss hadn't realized I was over 16 and he'd have to pay me minimum wage. When he found out, he fixed my paycheck--and mysteriously, I didn't have any hours after that. Huh. Funny. And this was when minimum wage was, like, $3.50 an hour.