15 openings, 15 moves deep, including possible transpositions that may have an impact on how the opening turns out? I think I have a pretty decent memory but it would take me a long time to develop that kind of memory/recall
Almost all my games are out of book by move 6-8 and out of the database I have by 12 (or close to it).
The time spent on trying to learn and recall all the variations will likely pay better dividends if spent in other study and learning the ideas/principles behind opening choices. Now, for those with phenomenal memories and recall, opening study might be worth it, especially if they are a fast learner.
I made it to USCF Class A on Opening Principles alone. I have 2 friends that are USCF Experts, and they made it on Opening Principles, and tactics. Obviously everyone has there own idea of how best to improve, and im just pointing out a few examples.