It seems so odd to me that they are building the birds after the carrier capacity has increased rather than meeting the demands for the capacity immediately. I guess the tech dev has it's own independent timeline.
They were surely building the flankers in paralel with building the carrier, for at least some time. Carrier itself started fabrication in 2013. parts for this third batch likely started their fabrication in 2017 or 2018 at the latest.
The carrier was handed over the PLAN in december 2019. First the crew needs time to even get acquainted with running the ship, before any serious try at getting used to operate an air wing. The ship itself also needs to go through another round of maintenance, which all ships go through after comissioning. US navy calls that period shakedown. For example, last Nimitz carrier was handed over to USN in may 2009. A month later it entered shakedown which lasted for almost a year. So in my opinion, the chinese carrier will also go through something similar and won't actually train with planes for at least another half a year or so.
The aforementioned nimitz also had to go through training its air wing and the crew, which took a year with the ship, so its first active duty deployment started in may 2011. Full two years after being handed over to the navy.
Shandong was checked for its airwing ops worthiness by the PLANAF with the original batch planes. I guess that could have been done with the new batch planes but that's not that crucial, as it's really a short series of tests after which there's another 6-12 months during which the carrier isn't really even available to actually train with planes.
As we now see, some of the new batch J15s are already produced and are being tested before final delivery. So i'd say everything is indeed on track for Shandong crew and air wing to start training with the new batch of J15s as soon as it goes back from the shakedown. It'll possibly be just half a dozen planes in the beginning, but by the end of 2020 there's no reason a whole dozen planes isn't available. And by end of 2021 there's no reason why a full airwing isn't being trained with. So first deployment may happen during 2021 or so and second deployment (first full strength deployment) sometime in 2022.
That's quite normal schedule, really. Just check out the British QE timetable with the F-35B airwing.