Do you think that this shows that the type 15 light tank really isnt necessary?
The Type 99A may prove to be less than ideal for warfare at Ladakh. But I think it is still wise for China to experiment with the tank at such an extreme environment. There are many new things that the researchers could learn when the tank is exposed to it.Not to mention that Type 99A showing up in high altitudes doesn't mean it's above 4000m where the confrontation sites are. Maybe it's just as useless there. It also doesn't mean it'll be as mobile as Type 15 even if it could potentially operate in high altitudes. That means they are very different tools even if they are fighting alongside one another which I honestly think is unlikely for extreme altitude. Type 99A and other PLA MBT all pass Tibetan plateau training but those altitudes are far more manageable than Ladakh.
Well this question is off topic but I'll try my best to answer. Looking at the Armata project, it seems like the biggest problem is procurement in large numbers. If China ordered them(probably in the hundreds), it is unlikely that Russia can manufacture enough to deliver on time(not sure why, maybe sanctions or financial problems).
Why buy a foreign tank? Is 99A not good? Even IF the PLA is not 100% satisfied the 99A, they still should focus on domestic products when possible. Fostering domestic weapons development programs and industries is now China's #1 strategic goal. It is more important than any specific product.