The interview process was extremely easy. I, a U.S. citizen, attended the interview with my peruvian fiancee. The interview lasted a total of about 10 minutes. The only questions that were asked were: "Have you ever been to the US?", "Have you ever been denied a visa?", "How did you meet?", and "What is the wedding date?" Most of the questions were directed to me.
Tips:
Get there early. The line gets really long if you wait to long. If you get in early you can sit in the lobby while you wait instead of outside.