This is my favorite etude, because of that soulful melody in the middle section. The rhythmic shift for the repetition is also intriguing.
Slow practice is necessary just to get the notes right in the beginning, but it won't guarantee success. What is needed is to learn how to support every single note in the arpreggios so that each note is securely and efficiently produced. It is the doubles embedded in the arpeggios that make it so difficult. That requires coordinating the entire body to achieve the desired musical end. In other words, it requires advanced technique, and it must be built on a solid foundation.
I struggled with this piece for years without making real progress. Then, a year ago, due to a serious injury (caused by unwise attempt on another Chopin etude), I went to a teacher to rebuild my technique, literally from the ground up. I am not up to playing Chopin yet, but I think I have a much better idea of how to approach this etude when I do get back to it. It will take the full deployment of everything I've learned about coordinated, tension-free, balanced, efficient playing.
In short, I don't think slow practice or endless hours of practice will give you success with this piece, unless you have a solid technique to begin with.