Not to pick on you, but I don't really understand the "how many should I rank" questions.
A standard rule for me, which applies whether you're doing a competitive specialty or not, in a competitive region or not, couple matching or not, or have other specific "complicating factors" or not, is:
1. Rank any program you could see yourself at for the next n years, given that:
2. You would prefer to be in that program for n years than not match anywhere.
There are fewer and fewer open spots in the scramble, to the point that I think you might as well assume scramble = no residency for you. It doesn't of course, but I think it is rare that your scramble is going to prove better than your bottom-ranked program. This is especially difficult for a couples match applicant- scrambling WITH someone else at the same program/region is even more unlikely.
If that doesn't help you, rank 15.