I think this is reading way too much into a few pictures. We know that the PL-15 is going to be compatible with the J-15T so it's a certainty that they will have access to them if they need to make combat sorties. The PLAN most certainly has trained in BVR warfare just as the PLAAF has, so it's not as if they don't know how much of an advantage the PL-15 confers. The only reason for these planes to not use PL-15s at all would be if they have something even better.
The PLAN is pretty conservative in its purchasing decisions, so even if they have something better in the future, they will still buy plenty of PL-15 as a stopgap. The other factor in this is that while some militaries treat the super long range BVR missiles as something special, the PLA tends to treat them as regular munitions and wouldn't be worried by price or anything like that.Well the radar is only as capable as the missile is in the grand scheme of things, plus the PL-15E is not particularly a competitive piece of equipment in light of the AIM-260, Meteor, and even the Astra Mk. 3.
If the PLAN really did not purchase or does not plan or purchasing PL-15s, the most likely explanation is that it's waiting for something new, either a particular launch platform or a new missile altogether (PL-16 for example).