Do you know 100% for sure your interview is waived? Only way to know that is either you get Decision Made, or your GCMS notes say so.
I wouldn't rely on the fact that you got PPR as a sign that it is waived because there are quite a bit of people who get an interview letter despite PPR. They just simply get their passports back with an interview letter and no visa.
Also I agree with ImAbule, I'm quite surprised you only sent in 12 pics on your app, especially given how difficult Singapore VO is and how important a spouse sponsorship application is, one would presumably want to send in the best app they could possibly make.
My wife and I sent 400+ pics, 350 of them were not the exact same, they were done on different days or same days but different events. The other 50 was just on the wedding day alone. It might sound like overkill, but given Singapore's reputation as a difficult VO, we didn't want to take our chances.
Hope you really do have the interview waived, however.