Bad enough that silent mode is gone - but with my upgraded Galaxy S5, the new lollipop Priority Mode is also not there ..... checked everywhere, rocked volume control,sound settings
You should be able to find it under Settings --> Sound & Notifications --> Interruptions. From my understanding, Priority is one of the 3 Interruption modes. You have Normal, Priority, and None. I have a Nexus 5, so this option might be different, but I can also change it from clicking volume up/down once and in the volume slider menu is now the ability to directly set the Interruption mode.