As a new healer, I can tell you already that it's night and day. Healing people in 10-14s is way, way harder than those in 15+. The people in 10-14s are the worst kind of players -- decent enough to know they're not bad, but not quite decent enough to understand what does and doesn't need to be interrupted; how to properly maximize survivability and are often the first players to start the blame game once something goes south. Playing a Shaman healer is actually extra irritating because even though it's the only healer with an interrupt (which is super nice), players apparently expect you to interrupt literally fucking everything because if a cast goes off that you could have interrupted, it's immediately your fault. Kind of frustrating but you learn to live with it.