Its hard to say if 15%-20% is high. It might be a little high, hard to say. But there are also those with other connection problems that I don't experience and could be related to the same issues. There has been a fair amount of feedback from people on this forum and other forums about the problems. We also need to take into account those who don't ever both visiting the forums to explore this issue.
I have played on a few different servers with my friend with whom I was talking to over the phone and I repeatedly got disconnected and he didn't, nor did anyone else that I could tell from doing a refresh on the server and still seeing everybody on it.