I guess that,for a 55-tons-MTOW level( 1.5 times of J-20 or F-22) fighter with great supersonic performance, if you want to take twin-engine design, you must have a Ultra-low bypass ratio turbofan engine with 1.5 times performance of F119, or you need an adaptive cycle engine which is even more powerful than developing XA100/XA101(200KN afterburner THRUST). Maybe China is not confident that they could develop such an advance engine in time, so they take the three engines design, and they can meet the thrust demand with three WS-15 engines.