By this point, the general consensus seems to be that the J-15 has filled its role as a temporary solution, and that the PLANAF is looking to acquire a next-generation carrier-borne fighter. Whichever aircraft will succeed the J-15 likely won't be the J-31, but will likely still be produced by Shenyang.
The J-15 is big, but its large size isn't only reason to induct a new model of aircraft. If the PLAN wants to compete with the F-35, then they'll need to come up with something of the same generation, at the very least, so an upgrade in all aspects is required.
Sure but even the US Navy still mainly operates the F/A-18E Super Hornet. At best you see the F-35B in use with the Marines with a limited capability. There are F-35A stationed in Japan I think but those are not exactly in China's main interest area (just look at their Northern Fleet, it is not where they put the Carrier). The F-35C will enter service soon, but it is still not in operation. Is it worth it to develop a new fighter for the STOBAR carriers? Or should they just keep working on something better that is explicitly designed for the CATOBAR carriers which are under construction? By that time the WS-15 should be available for example.