I don't know whether PL-15 size is small enough to be quad-packed on UVLS? and PL-15 range is 300kms?
300km?! No chance. Seeing as PL-12 is about 100km depending on launch altitude and speed, maybe +/- 50km (yes could be by that much) and how are we defining this range? It could be at the 100km range, the missile has so little energy left, the only realistic chance it has on achieving a kill could be by pure luck that the target happens to sit there waiting for it.
Quad packed onto a surface ship's VLS, there is no chance these missiles can get anywhere even close to 100km with today's tech. AIM-7, Aspide, AIM-120 all have longer ranges considering updated modernised versions and when used on a ship, even with some booster rockets, they don't even approach 100km range. So suppose a PL-15 really has 300km air to air range (quite unrealistic), if it gets quadpack VLSed, it's SAM form range won't even be half of its air to air range. Fitting it with serious rocket booster will cost space, weight, and complexity. If it were easy and worth the squeeze PLAN would have SAMed and quadpacked the PL-12 long ago.
I seriously think PLAN's defence layers are just settled for now on HHQ-9, HHQ-16, HHQ-10, and Type 1130. ESSM sort of fits in between HHQ-16 (latest versions with close to 100km range) and the HHQ-10. Maybe they don't see a point covering this gap unless a SAM version of the PL-15 really offers some enticing benefits. If anything they'd be far more interested in giving whatever extra space exists on 055 to BMD missiles or ultra long range missiles with 400km+ slant range.