Most people wouldn't remain at $8/hr their whole life, you would likely earn more as you gained training and experience. My point was that at the extreme low of full time wages, your savings rate at an early age helps determine where you would end up. It's doable especially at hire wages.

When I was making that kind of money, I still saved way more than 5%. Granted, after inflation, it is like $11.50 now. Still, 10% would have been pretty easy. 20% would be possible if I didn't blow money on things like spend $3K on a bike for hobby use. Also, that's assuming you don't have unexpected expenses. I lived somewhere where having a car wasn't necessary, so that made a huge different in budgeting. And when I needed surgery, I was lucky with insurance. Otherwise, that could have easily have eaten up the savings I had.

So 15% is definitely possible... with lots of luck and good circumstances.