something to think about, 15lbs of thrust is at the limit of what large EDF can do. Thats usually quoted in a pod, not in a ducted installation.

Secondly, although JL size F15s such as the avonds, yellow or skymaster do fly on 12lb thurst jets, theyll stagger around.
with P80s, theyll fly better but thats seen as a minimum. As F15s are so draggy, as you go up to 24lb thrust engines etc, the top speed probably isnt much faster than the 18lb thrust versions, but the vertical performance is better.
Most of that size F15s weigh between 20-28lbs, average it seems is 24lbs dry.(from straw poll of looking through jet mags)

I dont want to rain on your parade, but i think if you wanted any kind of performance, youll need two fans in there.