This whole him having a job is great stuff is pathetic. When I was 15/16 I had two part time jobs (nearly everyday after school and weekends) I'd work a 9-5:30 job every saturday and start my other job at 6. I was still studying year 11 at the same time and maintaing a (not exactly perfect) but an acceptable grade average. All of my money went to herps or my mum. Plenty of my friends seemed like your son. Half of them left school in year 10 and had no respect for their parents. He's probably just being a sheep.
You seem like you know what needs to be done, definatley toughen up on him. If he thinks he can just do nothing because he works then he needs to learn.