Perhaps a trivial question: why hasn't the PLAAF considered inducting the J-15S instead of the J-16?
At this stage we do not know whether J-15S has the same capability of avionics as J-16... or if it is merely a two seater of the standard J-15 (whose avionics are less capable).
J-16 may also have more structural strengthening to carry more load compared to what can be accomplished on a carrierborne fighter which requires folding wings.
So the question is not "why hasn't the Air Force considered inducting the J-15S instead of J-16" but rather "why should the Air Force consider inducting the J-15S instead of the J-16"?
Or even a better question: will the J-15S serve as the PLANAF's "J-16"?
The J-15S should already include the avionics/electronics and airframe enhancements found aboard the J-16S, as well as the 14-ton WS-10, but with the added benefit of canards. The specialized landing gears could be removed to save weight.
I expect a J-15S variant will definitely serve as the Naval Aviation's two seater strike fighter (and possibly with EW as well) aboard carriers, but whether the current J-15S will do so is another matter, as we do not know if J-15S has J-16 level avionics. If it only has J-15 level avionics then they will likely require a new J-15S variant.
I can envision a catapult compatible J-15B with fully new 4+ generation avionics (AESA, new datalinks, new cockpit, etc), with an associated J-15BS as well.
If you are not talking about Naval Aviation for carriers but rather for land based Naval Aviation, then if they do intend on operating a J-15S variant from land, I doubt it will have any modifications. I expect they will either standardize their land based Naval Aviation to be fully carrier capable, or operate a mix of carrier capable aircraft as well as dedicated land variants such as J-16s instead. I can't see the logic for removing the carrier compatible landing gear for a J-15S if one wants a land based variant. Simply operate it as standard from land without modification, or buy a standard land based only J-16.