The 15 etudes of Op. 72 of Moszkowski are not graded progressively by difficulty. And while I agree with other posters that some are more difficult than the others, I believe a more useful way to understand them is to know the focus of each piece.
Acquiring a good technique on the piano is both a science and art, and opinions on pedgagogy is highly subjective. So the following is my take on the Moszkowski Op. 72:
No. 1: single-note finger passages, primarily RH; Czerny-like
No. 2: single-note finger passages, primarily LH
No. 3: chord passages/rotation; RH=LH
No. 4: wrist; RH=LH
No. 5: single-note finger passages, primarily RH
No. 6: single-note finger passages, chromatic, primarily RH
No. 7: broken chord passages; RH=LH
No. 8: double-notes/wrist/rotation; RH=LH
No. 9: octave; RH=LH
No. 10: weak/outer fingers; RH=LH
No. 11: single-note finger passages, broken chord, primarily RH
No. 12: single-note finger passages, weak/outer fingers like No. 10; RH=LH
No. 13: double-notes; primarily RH
No. 14: broken chord passages using all 5 fingers continuously; RH=LH
No. 15: double-notes; RH=LH
I personally find the musical substance in these pieces to be uneven. The most musically satisfying ones, to me, are Nos. 2, 6, 11, 12, 13 and 15. I find No. 10 rather silly and pedestrian, although technically it has helped me a great deal. Moszkowski must have been a very good teacher to write these exquisite piano exercises!
Hope this helps.