I wouldn't class the Debussy as Romantic, though I get the similarities dizzyfingers points out. And Ravel and Debussy are as different as Chopin and Liszt, so if you're more confident with Debussy's style of writing perhaps look at other options by him- maybe Hommage à Rameau (Images 1) as a breathing space between Chopin and Scriabin- it's the same duration as L'isle Joyeuse so wouldn't spoil your timings.
I see what you two mean now. I have about equal experience with Ravel and Debussy but the Ravel just looks much harder
Is my current order fine? And do you have other suggestions for what to fit in the middle? I'm looking for something not SUPER challenging, I thought of a Debussy prelude but I don't want to have another prelude and especially not in the middle of my performance. Unless that's not an issue?
Another idea is maybe replacing the Scherzo with something else, would a Ballade or his Barcarolle fit any better with L'isle Joyeuse? Or anyother romantic composer, though I prefer Chopin like most pianists

I'm not in a rush to start LRSM (Basically just anytime before 2027) so I'll probably be switching things for a while before I commit to anything.