Confirmed with Leap 15.5 on a 2021 PC with AMD Ryzen 9 CPU. 22 seconds from Grub's "Attempting to decrypt master key..." to the openSUSE menu. Adding a key slot with iter-time 4000 and pbkdf2 and removing the old key slot doubles the delay to 44 seconds, confirming the issue is with the time to open the key slot. Repeating this with iter-time 60 reduces the delay to below one second.