I don’t think it is within Chinese military doctrine to withdraw J15 which is a new aircraft to training role, that would be a huge waste
it will serve the PLAN for years if not decades to come
I didn't say that the PLAN will/should withdraw ALL J-15s - Only the J-15/As.
We've seen this one from yesterday, where nearly half of the J-15s in this photo are the newer J-15Bs.
Hence, it is reasonable to deduct that the J-15B is already under at least some degree of LRIP, if not proper serial production at Shenyang AC. Perhaps sooner rather than later, there will be enough J-15Bs available for deployment across all three current PLAN CVs.
The introduction of J-35s onto the PLAN CVs in the next few years also meant that the need for more units of the J-15 family will become smaller than before (since the number of fighter parking slots onboard CVs are fixed).
So yes, it is reasonable to gradually relegate the J-15/As for training duties on land.
Also, it doesn't really matter if those J-15/As are new-built - They are quite outdated compared to the J-15Bs and the US counterparts (i.e. F/A-18E/Fs) today, let alone having to face the 5th-gens (F-35), 6th-gens (F/A-XX, GCAP) and the system-vs-system aerial warfare in the coming years.
TL; DR - Without some serious MLU onto them (of which the money and efforts associated may be better spent towards building more J-15Bs), the J-15/As just aren't gonna cut it anymore.