I second the parent. I did go to community college at 15 when high school didn't offer the opportunities I wanted, and there were basically 3 groups of people there:
-Underachievers, who couldn't get into a 4 year school, and their parents didn't know what to do with them.
-Underprivileged, who are working hard to be there and take it seriously, and might be anywhere from 18-50 years old.
-Underaged, who are bright but not ready to move away.
Honestly, I preferred my CC days to my undergrad days. At undergrad, the underprivileged aren't there (by definition), but the underachievers still are; they just have more resources to waste from the same parents that put them in SAT prep classes. This results in a much lower signal-to-noise ratio, and a much worse environment (at least for the first year or two of undergrad).
And on that note, I think that the overachievers at 15-17 should be sent to CC, where they will move faster (and more flexibly) than in high school, without the responsibility and risks of undergrad.
Other commenters below are saying that these students should be sent immediately to a "real" school for the proper "environment". Let me ask you: unless you went to a place with a culture like MIT (not my alum), were your first 2 years of undergrad really a good academic environment? I had many more negative environmental influences on my studies at my undergrad institution than my CC, and I've yet to have a friend report differently (including at Ivy League and tech schools).