Also, the ZTQ-15 purportedly has frontal protection at least in the 200-450mm range (some sources state it's protected against 3BM42 125mm rounds), where 200-450mm reflect the penetration ability of the 3BM42 at differing angles. Noticeably, the ZTQ-15 doesn't claim to be able to protect against Lekalo 3BM44 which has a claimed peak penetration power of 650mm, although modern Vacuum 3BM69/3BM70 has a claimed peak penetration power of 1000mm/900mm depending on whether it's running DU or Tungsten.
On the positive side, the level of frontal protection the ZTQ-15 has is roughly comparable to that of old T-72s without ERA, so you can see how technology advances; the ZTQ-15, a light tank of 2015, is superior to a T-72, an MBT, that went into production in 1972.
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And lastly, remember this entire thing is in mountainous terrain. If, say, a ZTQ-15 is hosted on a slope somewhere where it can get a clear shot at the top of a T-90, the T-90 is toast no matter how good the general ERA is. 3rd generation tanks in general have terrible top attack protection. This is possibly why the PLA stuck to 105mm; even 105mm is adequate for engaging enemy MBTs in mountain warfare provided you have a sufficient height advantage.