I can't tell if college is actually worse. Instead of social anxiety, in college so far I've substituted avoidance to avoid the SA, and it's worked. After introductions on dorm floors after the very first couple weeks or so nobody really cared about what I was up to and left me alone because I didn't make myself accessible. For the past two years I haven't made any real friends as I've spent and constantly spend a lot of time away shut off from everyone else in my room. This has actually lowered the amount of anxiety and stress in my life by a lot.
As a sophomore in college I very much agree with this ^. In high school you have to see the same people everyday for 4, 6, 12 years sometimes and you really can't effectively hide. You're sort of forced to build relationships with people, and an aspect of that is socialization. College on the other hand, like Tigerlilja said, after those first few weeks no one really notices or cares about anything you do, if you want to be left alone it's extremely simple to accomplish. High school and College are sort of polar opposites for me, I'm coming from a small high school with 250 graduating class to a college campus with 12,000 students on it so the difference is felt very profoundly to me.
Not sure if it makes it an easier or harder place to have SA though. Personally, what makes High School seem like a harder place is it makes you confront your fears everyday. In high school there's a lot of things going on too, and SA is just one more thing that you may feel you don't need. I think this is why a lot of people "grow out it" after high school, all that other stuff that was so important in high school isn't anymore, sometimes one of those things is SA and when it isn't it allows the person to work on that issue now that the others are gone.
But I don't think it's the High School that makes it hard, but confronting that makes it hard, which after high school you don't
have to do, either because you've grown from high school and it's not an issue anymore, or you're effectively able to avoid it. Basically what I'm saying is SA is hardest when you have to confront it, whenever that is.