Here's a great article that appeared in Forbes about the archaic and arbitrary 15 minute doctor visit. It's a nice validation for why our clinic schedules 30-60 minutes per patient as standard.
To take things further, the article doesn't even mention that the problem even goes beyond this: it is common practice in actuality to spend only 10 minutes with the patient during a "15 minute" visit!
(If you want to know how/why, it's a bit complicated, but here's the gist: doctors are not actually required to spend the whole 15 minutes to bill that amount - completing all the necessary components during a visit will also qualify for that amount (eg. a certain number of questions, physical exam findings, etc.). In offices that are very streamlined, doctors can hit all those requirements in 10 minutes or less.)