I have 3 teenagers (and a 6 year old) and the homework load and sleep deprivation is a familiar challenge, add sports and their social life and frankly its astonishing what our teens handle. My number one goal with my teens is to help them listen to their own intuition and stay in touch with their own limitations, boundaries, and balancing their lives. Not giving advise and my own solutions but helping them find their own.
That being said, there has been many a conversation beginning with "how's that working for you?" If my teen tells me he/she is overwhelmed, I ask questions and listen more...until he/she comes up with their own revelation as to what is too much, where he/she can make changes, where he/she wants to make changes and am always willing to help them acheive their solutions.
Sometimes they need to have frank discussions with their teachers, sometimes they need to be realistic regarding the academic load and need to change classes, lighten the load. Their mental and physical well being is not worth pushing beyond their limits.
I've found, its really important for them to have an enjoyable experience with school, where they can handle what they are given and still feel challenged. Teens know so much more than we give them credit for. Listen to what you're teen is telling you even if you have a totally different take on things, and honor what they are saying. Walk through their plans with them, curriculum, sports, arts, other interests and ask which is most important to them right now, know where their hearts are, help them get in touch with their own hearts. After that its a matter of guiding them through to their own solutions and letting them deal with the outcome. I'm just happy my kids are learning to trust in themselves and feel they have a great deal of control over their own life and what they make of it.
If I were you, I'd find out what your son wants to do, what would he change? Etc...Then support him with those changes.
I hope this helps in some way.
M.