15 year old adhd child will not keep clean

I went to school with boy who sounds very similar to your son. Sadly he had no friends and was teased a great deal amount. At the time I couldn't understand why he chose to be that one. Now that I'm older I understand better. His parents were kind, owned their business and his father was a policeman. Since he has to follow a routine, I'd simply start adding another bath or shower into it. People need to be able to adapt to change no matter how difficult it is or not. I don't mean to pry or sound ignorant but because of his ADHD and Autistic Spectrum Disorder does he have to meet with any professionals/counselors? If so maybe they could help him understand the importance of grooming himself and having good hygeine routine. If not..maybe rewarding him for his effort in some way would help. He needs to learn to care about himself and to have good self-esteem.

Bless your heart. When my son was that age (he's mild undiagnosed Asperger's), he went through a period of about 6 months when he didn't want to bathe too often either. And he had read on the internet about the bad effects of an antipersperant/deodarant. Fortunately for us, he loved the youth director at our church. (She as a woman just a few years younger than me who had a son my son's age.) She took him to the store one day and asked him what deodorant he liked and bought it for him. There was never a problem after that. In fact...the following year, he took 3-4 showers a day.