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.
The IRS says you have to report illegal income and pay taxes on them.