I'm assuming your outlets are 120V, not 240. If not the case, then ignore this.
Your best bet may be to pull the outlets out of the wall (Shut the breakers off and test them first) and see how they're wired.
Chances are they're split-phase; the RED goes to the TOP, the BLACK goes to the BOTTOM, and the WHITE is Neutral for both. That can only be confirmed visually or by using a breaker finder like the IDEAL 61-532.
It's also possible the electricians just ran three-conductor wire to save on cost, and just passed the red (or black) wire through to other outlets.
By "Double 15 amp" do you mean DUAL POLE? Or just two switches in a single space?
The latter case is very common, and yes, you'd need two CT's per SPACE (it's still a single CT per "Breaker," though, since it's really two breakers inside one case.
You do not need dual CTs for GFCI breakers.