The greater blessing will be 15 those were added in patch 1.9.
New, 15-minute raid versions of blessings, and the ability to bless all members of a certain class with one click
Paladins can now learn Greater Blessings for the following spells:
Blessing of Might
Blessing of Wisdom
Blessing of Kings
Blessing of Sanctuary
Blessing of Salvation
Greater Blessings will cast the associated blessing on all raid members that share the same class as the target. For example, if you cast Greater Blessing of Might on a warrior in your raid, all warriors in the raid party will receive Blessing of Might from you. Additionally, Greater Blessings have an increased duration of 15 minutes. These blessings require twice as much mana as the single target version, as well as a reagent. Paladins can purchase these new Greater Blessing spells from their class trainers.
This is among the reasons the original devs literally called paladins a failed class. They and their shaman friends are often Exhibits A and B for why class tuning should be considered for the upcoming servers.
That blessing rocks though, and the difficulty with the uptime is totally worth the stress IIRC.