Like a lot of others, I've been there too. Things that we'd have never done are now considered normal adolecent behavior. Only advice I can give is to stand your ground. Your house - your rules.
When he was 15, my step-son drew back on his mother. She spun around and decked him (she's 5' 1"). When he got up off the floor, he threatened to call social services or whatever it is called. She looked up the number and handed him the phone. It was a tough few years, he finally quit school and went to live with his father. I was really ticked that he quit school, but told him that if he thought he was a man, then he could live like a man. His mom and I had our moments, but stood united.
About 2 years later, he apologized to both of us for the way he'd acted and I couldn't have been prouder of him.
Fast-Forward to today; he's 34 and still feels badly about his actions and the strain he put on our marriage. Now he's got his own 15 y/o starting with the same problems; low grades, bad attitude, etc.
I wish there was an easy answer. Just make sure he knows you love him and only want what's best for him. Remind him that you've been 15 too and have experienced some of what he's going through. Be there for him when he wants you to be and let him be himself when he has to be. Then hope & pray that he grows out of it sooner rather than later.