If you are required to have an interview, it is because they see something in the file they want clarified, even genuine marriages have been questioned, and if you are waiting the 11, 12 and even 14 months for an interview, even before knowing if you will be interviewed, you should be spending that time preparing in case you are interviewed. There will always be things that you will not know about each other, things that don't come up in everyday conversation, but from the time you meet each other until the interview is more than enough time to prepare! I assume the sponsor will always believe the marriage is genuine, but unfortunately there's going to be times where both people don't feel the same. I have heard of many people passing their interviews in santo Domingo, and many people being denied, mostly because of age differences they don't think it's love. I honestly feel like they see the age difference and assume it is only for a visa, maybe they know they will deny them right away but must grant an interview. I also read that if the sponsor doesn't attend the interview, they think they aren't supporting each other.
I was lucky enough not to need an interview, and I know if we would have been interviewed there are many things in life me and my husband don't discuss, and I know we would have had trouble, but it doesn't mean we don't love each other!