Focal Electra 1038be owners,

Room size has little influence except for subs, 90% is seating distance.

Focal states 93dB sensitivty, but Stereophile and SoundStage/NRC have shown other Electra Be models to be about 3dB lower than spec, so 90dB, which is still above average.

Room gain for a tower speaker is about 3dB, so back up to 93dB; seating distance of 15ft is about a 9dB loss, so now 84dB.

If you want peaks of 100dB, you would need +16dB, which would be ~40W.
Now, it’s not good to operate at max wattage all the time, so I would say a 75W amp would suffice (again, assuming wanting 100dB peaks).

Now, it’s impedance drops pretty low and for bass frequencies, so I would suggest getting an amp that states 150W+ into 4ohm.

"listening position about 14-15 ft away"
Unless your room doubles as a living space,
distance seems excessive.
Your ears are the final judge. My room is a little narrower-13'4 and longer-28'. I use the Cardas setup. http://www.cardas.com/room_setup_calculators.php
Not for everyone, but I find it the best compromise for all the audio geek sonic requirements. Room treatment, along with the Cardas setup, gives my midfi setup a  boost more than cable madness and ridiculous tweaks.
The Focal 1038's are great speakers. They are on my used list radar.I presently have speakers with dimensions not far off from the 1038's.

Based on the calculator, speakers would be somewhere spaced between 6-7' apart, so your listening sofa would be positioned appropriately for that distance. Unlikely 15 ft away unless, your dealing with living space compromises.
In the end, trust your ears.

They will be fine in a 14-21’ room. 

Great speakers, especially at current clearance prices.  I play my 1038s in a 20’ (wide) x 30’ (deep) x 9.5’ (high) area of an open floor plan (family room/kitchen).  Listening position is about 9’ from the speakers, which are about 8’ apart and 32” from the 20’ wall.  Hope this helps.

I have a pair in a room 16 x 26 x 8.5. 
It's too live for my liking, and optimal placement is not an option, but imo it's certainly big enough, and I would suspect your room is big enough as well. 
I considered both the 1038's and the 1028's, and I'm glad I went with the . 1038's