It seems like currently Unity Editor don't understand the data layout of complex Fbx model and make the importing so slow. The import time looks like same even the fbx has animation. I think this area really needs to improve as if I have 100+ fbx model like this then I need to take a decade to upgrade the project to each new Unity release. Furthermore, just change a setting like switching to Use External Materials(Legacy) or Extract Material with Use Embedded Materials also takes almost same amount time to apply setting which is unacceptable. Seems like regardless of which setting will ends up reimport the whole fbx.