I would say that under "normal" circumstances it shouldn't take more than 30 seconds to a minute to back up a catalog with that many photos. But since you have indicated that you're having performance problems, you're just have to try it and see.
I don't take R rated photos or photos of questionable suitability. But as I think about your situation you might want to consider separate catalogs. But that is something for you to figure out for yourself.