What might prevent a mobile build of a VR game from being successfully built if the Player Settings API Level is at 16?

When considering the Player Settings API Level for mobile builds, the correct interpretation is that a minimum API level set to 21 or higher will prevent a build from being successful if the current API level is only set to 16. In this context, the minimum API level indicates the lowest version of the Android operating system that the application can run on. If the minimum required version is higher than the configured API level, it leads to compatibility issues, thereby causing the build process to fail.

In mobile development, especially for applications like VR games that often involve more advanced features and capabilities, ensuring that the API levels are set correctly aligns with the hardware and software requirements that the game needs to function properly. Setting the Player Settings API Level lower than the minimum required level thus creates a scenario where the game's foundational functionalities might not be supported, which is critical for VR applications where performance is paramount.

This understanding of API levels is crucial for any mobile development work, particularly when dealing with VR where the demands may require targeting more recent versions of the operating system to ensure compatibility with device capabilities and VR SDKs.