$15 for 3 months? I've never bothered to look at prices for the "Not a full year" cards before.. but that sure doesn't sound like much of a deal, even if it's a discount from normal.
These can be a deal to some who do not need live continuously. Lets say you skip a month of live because you don't use it. When my live runs out, I only put in a new code when I absolutely need it.