Scott,
When I was full-time in the biz, I paid my groundies 15 bucks an hour.
When I started I was a one-man show. Eventually I forced my younger sister into indentured servitude to work the ropes for me. She was a great groundie, one of my best.
I trained two of my guys from groundie up to climber, and my top paid climber was making 25 bucks an hour when I shut everything down. The economy was better back then, and I was also making a good chunk of change with timber, so I didn't mind paying my men well.
The one drawback I could see would be the license. I can see that being a hastle if I needed you to run a load somewhere or drive a truck, or whatever, but if you are on time to work and perform your duties satisfactorily, then that shouldn't provide much leverage for your boss when it comes time to talk money.
Maybe your boss is hurting for money. Even making 4k a day, he may have over-extended himself and found himself behind the 8-ball, financially.
A good climber is worth more than 15 bucks to me. It sounds like your more a foreman with all you are required to do. Running his daily operations while trying to feed your wife and 4 kids oughta be worth more than 15/hr to him.
From Robert Greene's "The 48 Laws of Power"- Law 13: When asking for help, appeal to people's self-interest, never to their mercy or grattitude.
Basically what this means, is that you will make alot more headway with your boss by detailing ways that him paying you more will help his business, than by detailing ways that him paying you more will help you and your kids. As much as he may feign interest, he cares more about his busniess and his money than he will ever care about you or your family, and you need to find a way to show him that paying you more is an equitable investment in his business. How you pull that off is up to you.
Good luck,
T