I can confirm this problem with Oticon hearing aids and iPhone 15. This problem has been driving me crazy for months since upgrading to iPhone 15. I could not access my voice mail because the phone tree kept saying that the passcode was incorrect. The voice mail carrier was able to prove to my satisfaction that the problem was not on their end. Called AT&T, then Apple. No luck.
This morning, before I put my hearing aids on, I had the crazy idea to try accessing my voice mail without my hearing aids on. Holy cow, it worked! And when I put my hearing aids on and then tried again, the problem returned.
Apple should fix this. But until then, rjfedora's workaround works!