It's not affected the mantra of healing itself - i.e not the HPS.

It only affected the rune - boon of protection.

If I read it right, it will give you a shield that absorbs damage up to 15% of your life for the first 2 seconds after you activate it. So if you "spam" it (no CD, but costs 50 spirit), it will give pretty much a shield to absorb the blow. Since it's 15% of your life, if you run high vitality, it will absorb plenty. (changed now to the same amount of 3 ticks of mantra of healing, right?)

...but it's not taking away that that Mantra is another one of those heal when needed