It's a big convenience for carrier ops. Iirc, last batch of su-33 also has internal ladder. J-15 of course has it.
Two of them.I'm pretty sure J-15 does not have an internal ladder.
All these years I can't ever recall a J-15 with an internal ladder used.
As for Su-33 I cannot recall seeing such a thing either but I also pay less attention to that type of aircraft so I'd be happy to be corrected.