The most significant bit would be the catapult-related modifications. Now, looking at Google Map the training facility's catapults seems to be almost ready, how long would it be before there's a picture evidence of catapult launch?
Who knows, maybe very soon or maybe never.
Keep in mind, the chances of us getting a perfect satellite image for Google Earth which shows a J-15 launched from the catapults at the test facility being launched is pretty low. After all, GE only updates every few months (if at that), and to prove what you describe, will need to show an aircraft perfectly lined up on the catapult at the facility at just the right time for a satellite to take an image that will just happen to be integrated into GE's services that will let us see it. The chances are just so low.
The highest chance of maximizing our chances of catching it is if someone buys out a LEO satellite to constantly monitor the NATF base at Huangdicun... but obviously only a few countries and companies have that sort of resources.
So we should all accept the likelihood that we may not get satellite photo evidence of J-15As being launched from the catapults, because the way that Google Earth and other similar applications work means we need the luck of the draw for a satellite to just happen to catch a J-15A near the catapult at the perfect right time to fill all the boxes for confirming a catapult launch.
I think it is more likely that we will get an official PRC/PLA approved photo or footage of a catapult launch taken from the ground, before we get a satellite photo to prove it (if that even occurs in the first place).
We know they've planned for catapults from the beginning, other things notwithstanding they've keep the "shooter" as part of the launch crew, which is unncessary for a ski-jump carrier.
Nah.
Even on USMC LHDs, they have a "shooter" as part of the deck crew for launching harriers. If you search "harrier launch shooter" the first couple of images you get shows what I describe.
So the presence of "shooters" on the STOBAR carrier doesn't tell us anything about their plans for catapults, and it never should have told us anything about it.
What we know about their catapult intentions instead has all come from years of accumulated rumours, instead. Without those rumours, we'd be so far behind the curve it wouldn't even be funny.