Brilliantcp asks some good questions. Don't know if the OP is coming back, but I think every student should apply to at least one, preferably two schools where they are almost certain to be admitted. This means EA (non-binding and not SCEA) and/or true rolling admission schools where you receive a decision in 3-4 weeks. While these may not be top choice schools, they should be schools that the student would be willing to attend.
I did that with my two older ones, and will do with my youngest in a few years. Having an acceptance or two before the New Year means you know you'll attend college in the fall.
To the OP, you are right that students who graduate HS early may be at a disadvantage. I think that colleges fear that there may be social issues with younger students. Sometimes there are, sometimes there are not, but it is safer bet to go with the 17/18 year old with the same stats as your son than to take a chance on a 15 year old (unless he has some hook, such as groundbreaking research or is a top athlete).
If you are looking for good research universities, there are public schools that are very good research schools. If he has top grades and test scores, he should be eligible for Honors colleges within public schools, and those can be a great opportunity.
And even if he was 17/18, 10 APs and great test scores don't ensure anything. Middle kid had 10 APs (9 - 5s, 1 - 4), NMF, great SAT & ACT scores, some academic awards, 2 varsity sports, on the board of a non-profit, part-time job, etc. - did not get into any of her top choices (deferrals & waitlists, couple rejections). She is very happy at a public school, great research school. She'll be involved in some research next semester (in her freshman year). Also was admitted to a couple of schools with acceptance rates of about 25%.
Good luck with the process. If it does not work out, a gap year could be good. Don't attend any college classes though - not any community college classes either - if he wants to be considered a freshman for admission purposes after a gap year. Transfer admissions are typically much more difficult.
