A leaker with a good reputation but not an abundance of detail, claims to have been told that Apple's planned iPhone 15 cases do not include the usual leather options.
I've heard that Apple won't be releasing a Leather Case for the iPhone 15 series.— DuanRui (@duanrui1205) August 17, 2023
The leaker's history with cases and accessories lends weight to the claim, but Apple has shown no other signs of intending to stop using real leather. At present, Apple is selling 16 leather cases for the iPhone 14 range, plus around 18 leather straps for the Apple Watch.
Then there's the iPhone leather wallet with Magsafe, AirTag leather loops, and a leather Apple Pencil case. Add in the iPad and older iPhones, and there are many more leather items being made and sold by Apple.
It could just be that DuanRui's information is somewhat incomplete and really Apple plans to ditch all leather products. But sources knowing only about abandoned iPhone cases and not, for instance, a planned total removal of the material, makes it all seem unlikely.