The Green Head must be a bit better 'cause I ain't never heard of no one hurling a Green Head .23! . The .23 is a somewhat rare engine, isn't it? I'm just going by how much I've ever heard or read about them. I think it was intended as an upper displacement limit engine for class A free flight back in the day? Or lower end limit of class B?
    Type at you later,
     Dan McEntee

I use to use the K&B 19-23 for class A & B FF the 23 was a very powerful motor in its day. I used them on a Ramrod 600 and did win a few contest in Class B with it. I also used them in CL on Sterling Mustang and they flew them well. I think it is a lot more powerful than a Fox 15.
Ed

  I haven't run a Fox .15X in a long time, and the last plane I had one in was a SIG Acromaster. I really didn't know what I was doing back then and was probably running it on the wrong fuel and too much prop pit, but I remember it putting out enough power to really haul the Acromaster and get my attention! I have no real concept of the size of the profile Peacemaker, but if it's in the realm of the Acro in size, it would be adequate for the job if the correct prop for it were used. I'm going to have to duplicate that airplane/engine combo just to revisit it and see how it performs when properly executed. I'm thinking that any short comings of the Fox that others have had can be over come, and if not, try something else!
   Good luck and have fun,
    Dan McEntee

My two penn'uth - Fox 15X will be a nice gentle plane. Mild aerobatics on suitable length lines. K&B 23 will be a much meatier kettle of fish. (Excuse all the figures of speech). Longer lines, more speed.
If you have to fit a silencer, I  always figure the 23 as a good engine for a design which was originally for a 19. (Make it a light silencer).