My main gripe with the Type 15 is that compared with a tank designed with similar design constraints, the Japanese Type 10, it is just way too lightweight. Weaker gun and a lot of other stats, like the transmission, maybe even the armor. It will be barely competitive against current generation MBTs but will likely struggle against the next gen ones. China has a tradition of making these overly light tanks like Type 62 which in practice are highly vulnerable. From what I understand the Type 62, and probably this tank, have these severe weight constraints because they are expected to fight in the marshy jungles of Southeast Asia i.e. on Vietnam. This is also the tank that China might use in an island hopping campaign in the Pacific if it ever came to that. And in fact probably for that reason is already in use with the PLA Marines.
The ZBD-04A is an utterly obsolete design at this point. Russia is replacing its similar BMP-3 with Kurganets-25. Or they will once they ever get it into production. This is much more comparable to similar designs like what South Korea is using.
Given the terrain constrains China has, I think it needs two tank designs, one lighter, and another heavier tank. One for Southern China, and another for Northern China. So I do not think the Type 15 project was a waste of time, but the base specs were probably a mistake.