15 thousand kamikaze drones may only be enough for Taiwan. Having 24 million people squeezed on an island barely larger than Hainan would require a massive amount of transportation, telecommunications and energy infrastructures and facilities to be targetted.
Besides, apart from Taiwan, the PLA has to consider targets located along the FIC as well. Those would require at least hundreds of thousands of kamikaze drones, if not millions of them to be effective.
Furthermore, there is also the presence of specialized anti-drone SAM systems to consider. Having observed the developments of the war in Ukraine, seperatist extremists on Taiwan and countries along the FIC are definitely looking forward to equip them as well. That means the consumption of kamikaze drones would be significantly higher than what we've seen in Ukraine and also Nagorno-Karabakh.
In order to counter this, there are two ways:
1. Procure even more Shahed 131/136-like kamikaze drones; or
2. Procuring more capable kamikaze drones that can fly faster, can hug the terrain better, and with better LO characterstics.
Or you can do both.