Maybe it is indeed quite simple and so far the PLAAF has some sort of monopoly since until the J-15T arrived, no PLAN NA fighter was able to use them (at best the MLUed J-11BHG), so that they are not yet delivered to naval units?
I'm not suggesting that.
At this stage we have yet to see any J-11BG (whether PLAAF BGs or PLANAF BHGs) carry PL-15 -- in the case of J-11BG/BHG, PL-15 delivery may well be an issue of prioritization (J-20, J-10C, J-16 may have priority).
For J-15T, I am saying that as a new aircraft for the PLANAF that is almost certainly to have PL-15 as one of its primary weapons, the fact that we have yet to see J-15Ts with PL-15s could be any variety of mundane organizational reasons.
Putting it another way -- I do not equate J-15T and J-11BG or J-11BHG. For example, if J-11BG and J-11BHG are currently not tapped for PL-15s (even if they are compatible with them), then the J-15T would technically be the PLANAF's first fighter that is intended to field PL-15 as a primary weapon, and therefore the first reason for PLANAF to induct PL-15 to begin with.
As I said, I think being "surprised" at J-15T not having PL-15 (and indeed, as written in your tweet) is unnecessary at this stage and just ends up leading to speculation which may not be useful. Sometimes there are observations which are better left un-circulated because it just leads to potentially normal phenomenon being assailed as "strange".
If we go five years and don't see any J-15T with PL-15, then that would be a reasonable basis for questioning, but right now it's just too early.