Hi totally,
Having recorded Op. 23, No. 5 in Gm, I do know the piece inside out. Including the lyrical middle part, there are octaves and, more often, octave chords appearing in both hands throughout in nearly every measure. They also require various touches--nonlegato, staccato, legato, tenuto, forzando, sforzato and leggiero (no portato though). Because of that, the issue is not just playing the chords per se, like vertical skyscrapers, but rather it often lies in the horizonal voicing of the melodic line in the tops of the octaves and chords of the RH, which is far more difficult and demanding. To make matters worse, there are sometimes inner lines within the structure of successive chords that are far more difficult and exacting to voice. Pedaling too has its quirks, as there are often three-note slurs where the middle note must not be caught in the pedal. In general, I would tell you that this prelude is a very "athletic" piece requiring stamina and endurance. It's played with the body, shoulders, forearms and wrists (oh, yeah, sometimes even the fingers too). Having smaller hands would make it that much more fatiguing, especially as you mention that yours tire easily.
Rachmaninoff had three roles in life--conductor, composer and concert pianist. In our day probably Bernstein would be a close approximation, although their emphases were different. Rachmaninoff put conducting (at which he was absolutely superb) behind him earlier in life, whereas Bernstein spent most of his time conducting. Rachmaninoff composed a great deal more than Bernstein. And although Bernstein was a very fine pianist (Gershwin's Rhapsody in Blue, and Mozart Piano Concerti), he played relatively little, while Rachmaninoff early on made touring as a performing artist his livelihood right up until he died in 1943. His composing output diminished as he grew older, because of the time commitments for practicing and recitalizing on the tours.
Anyway, this is fact: Rachmaninoff (with his enormous hands), unlike say Mendelssohn or Chopin, didn't write his piano solo works for you, me or other pianists. When he would recitalize, he largely played his own piano works. So these pieces were the tools of his trade, thus he really wrote all of that music for himself. And where he was one of the greatest virtuosos ever, that makes playing his music all the more challenging for us.
None of this is to discourage you.
The Gm is graded "difficult", but when the time comes, try the piece out. If it's too daunting, and if your interest will be to entertain yourself rather than playing it in public, then there are ways to "simplify" the piece to better suit a person with small hands. It would be a big compromise, of course, and would not comport with the composer's intention. My observation over the years has been that pianists who are "purists" with smaller hands either avoid Rachmaninoff altogether, or carefully select his pieces that literally fall within their grasp--and there are some of those too, fortunately, in his repertoire. However, another thing I've discovered is that if I really love a piece, I'll take it on no matter what!! Sheer motivation can accomplish great things!
Enjoy your upcoming listening sessions!
Topic: Bortkiewicz, Prelude, Op. 33, No. 7 in F#