Yes but there are cheaper ones out there already that do the full 15w charging.
I have one of those many said cheaper ones that claims to do full 15W charging, yet when actually using it ... it doesn't. If you cannot charge up and use the iPhone simultaneously vs just use the iPhone with MagSafe-like chargers it's not something you wanna cheap out on (the latter).
There is an interesting thread here on that.
Magsafe Powerbank thread
Hi! there is no powerbank options widely available yet I'd like to track news here Right now I was able to find only this one - OISLE - seems insanely expensive and useless to me :)