Like I said, the 15 years means that the prototypes are flying. At least airframe, engine and basic flight test avionics.
As to advanced weapons ... the aircraft could have built-in growth potential to absorb them down the road should they reach a targeted weight and power need.
Like how the Zumwalts are going to sea with the 155mm AGS, but have enough electrical generating capacity to backfit a railgun.
Like how the Zumwalts are going to sea - both of them ...