But China does not yet have a fleet of aircraft or pilots ready for carrier operations. So the Liaoning is being used to test and train them, a task that experts say will probably take several years. http://www.bbc.com/news/world-asia-china-35207369
The J-15 itself could be considered only in the development stage. J-15s were only introduced in 2013, with only 21 built so far.
Much in concurrence with this Submarine Matters article and comment string is this article Why China's next aircraft carrier will be based on Soviet blueprints of January 7, 2016.