No. 557 ??!! Do we really have that number ?
I think 554 is confirmed, huitong mentions 557 possibly.
What was the reason for the speedy change, bad WS-10 performance in J-15s?
Maybe, who knows. But seeing as WS-10 was only fit on one, maybe two J-15 prototypes while the rest were Al-31s, suggests to me the navy wasn't intending on having the first batch of J-15s be powered by WS-10s in the first place.
Unfortunately we don't know what about WS-10 at the time may have been the limiting factor — everything from risk of corrosion to spool time has been considered and mentioned before — but we do know WS-10A is good enough for all new land based flankers produced over the last few years, so go figure.