Enable mip stripping for all platforms.
When enabled, strips unused mipmaps at build time.
When Unity builds your game or application, it can strip unused mipmaps from Textures in your Project. Stripping unused mipmaps can make the resulting executable smaller.
When Mip Stripping is enabled, Unity examines the Quality Settings for the current platform at build time. If a mipmap value is excluded from every Quality Setting for the current platform, Unity strips those mipmaps from the build. Mip Stripping depends on the QualitySettings.masterTextureLimit setup, and it will only affect texture types that are also affected by the master texture limit.
At run time, if you use QualitySettings.masterTextureLimit to set a mipmap value that has been stripped, Unity will set the value to the closest mipmap value that has not been stripped.