Spring Dance is a little less difficult, and the piano part in the middle is the hard part.
Ruslan and Lyudmila Overture, although simple, but long and not easy to memorize.
These are the ones I used to play, and I don't know if the repertoire has changed yet ......
All in all, the Carmen Overture is the easiest.
The Dance of the Flowers is also pretty easy, and candidates use it with Carmen a lot.
The Xinjiang Tour is a bit longer, but the difficulty is on the lower side.
I accidentally posted it just now before I finished writing it ......Sorry.
Good luck with the exam!