I'm not sure that anyone has proved a link between time spent doing homework and academic success. What matters is how effectively someone is learning. So maybe he could do a bit of learning every night instead of written homework, which he obviously finds boring. People learn best by doing something active and enjoyable.
Two things he might enjoy are:
Using kinaesthetic learning. In order to remember things use physical movements. I did this with my 13 yr old nephew who is very sporty.We did Spanish prepositions - in front, behind and so on. We used a chair and told each other to stand in front, behind etc. And then we did arm movements. I suspect we will both now remember our Spanish prepositions.
Also computer based learning, for instance on BBC Learning website is a good place to start.
Anger management!!! Help needed.