If I had to make an educated guess, I wouldn't say batch 3 is made exclusively to the Shandong... I'd imagine for redundancy purposes that all J-15s (especially since we've only got a handful of them), regardless of batch, are capable of deploying out at sea on both the Liaoning and Shandong. The carrier air wing concept/program is still somewhat in its infancy anyway.
According to Scramble (
), the PLAN only has a single carrier air wing in Huangdicun (alongside the Naval Aviation University where new naval aviators are trained), and based on the geographical location it would seem that it is assigned to the North Sea Fleet where the Liaoning is based in Qingdao. So perhaps they're using batch 3 to grow a carrier air wing for the South Sea Fleet, especially since the Shandong will be assigned in Hainan?