Actually, a significant portion of the money is being dedicated to prevention. The model used in Uganda , abstenance and teaching, has lowered the spread of this disease in that country. The black man sitting beside Laura Bush at the SOTU was the health official from Uganda who has pioneered this approach.
Unlike in the US, AIDS in Africa has spread to the general population. If the civilized world doesn't stop it there it will no doubt soon be upon our door and not limited to a certain demographic.
That shouldn't cost $15 billion.