Android 15 Beta is delayed because Samsung wants to have a shorter Beta period. They are insuring the 1st Beta works as smoothly as possible. Also, part of the delay can be from Google's end. They didn't ship the Pixel 9 series of phones with Android 15. While Google does give OEMs the OS early so they can put their skins on it if Google hasn't finished with the OS Samsung has no choice but to wait.
As far as the next feature rich drop based on 6.1.1, sometime in September.
