In terms of priority I think it's the opposite, WS-19 first, then WS-15, then WS-20?To be honest, I think we'll sooner see the Y-20B with WS-20 in service, or finally the WS-15 in a J-20, than the J-35 prototype is already powered by the WS-19. In fact I have no hope.
Wasn't there lots of fanfare a while back regarding some WS-19 breakthrough? We'll see how it goes but I won't hold my breath for it.
I think time is the essence. In terms of technology China will figure it out, just like semiconductor.