The original design of WS-15 was scrapped around 2013 and completely redesigned. That's why it has been delayed for so long. It won't see service until 2023.
Rumor has it that its thrust was originally intended to be 15 tons, but the new design starts at 18 tons. If that's the case, I can see J-20 reaching a maximum speed of Mach 2.6 while being able to supercruise at Mach 2.
It's likely to be a variable bypass turbofan, presumably with greater than 20 tons of thrust with afterburner. As WS-15 is scheduled to be in service between 2023 to 2025, I expect the new engine to surface around 2030.
China has finished the project evaluation stage of the sixth generation fighters, now there are some declassified proposals shown in some Chinese academic papers.
Rumors say there are eight proposals, the engineering stage project will start in 2025, and first flight of the 6th generation fighter could be start as early as 2028 (if we follow J-20's project, 3 years after the engineering stage project starts, J-20 conducted its maiden flight).
The fighters will equip with two-phase engines, laser weapons, advanced stealth features and cutting-edge AI system.
The following are believed to be some of the (failed) proposals for China's next generation fighter leaked in journal papers: