Reloader 15 for 223?

Yes.

Yes

Yes

That or Varget works well with heavy bullet.

I had some RL-15 laying around which I bought during a Varget "Shortage". Loaded up some Hornady 75 HPBT and they shot pretty well.

24.0- 24.5 gr. of RE15 and a Sierra 77 MK or Hornady 75 BTHP has been a go to load for NRA highpower service rifle shooters for many years. Out of a 20" service rifle barrel they usually run around 2750 fps. It is a bit temperature sensitive, in my testing figure around 1.2 fps of velocity change per degree of temp change.