The various derivations of J-11B do not seem unusual. Basically the J-16 would be the F-15K and the J-19 would be the F-15SE. The benefits of the latter being reduced cost for a stealth fighter-bomber and thus potential for more units. Since these would all basically be derivatives of the J-11 it isn't like producing three or four new fighters.
I mean J-15 is based off Su-33, which is a variant of the Su-27, and J-18 would apparently just be a stealthy version of the aircraft. Really the J-18 and J-19 would basically just be a navalized stealth Flanker for the PLAN and a stealth Flanker for the PLAAF.