So according to:
http://wiki.guildwars2.com/wiki/Rune_of_Sanctuary
(and in game matches)
The minor rune #2 gives: +5% Boon Duration
The major rune #2 gives: +10% Boon Duration
But the superior rune #2 gives: +20% Frozen Duration
I think it’d be much better if it gave Boon Duration instead of Frozen Duration.