Using GPU acceleration Resize Pro is the fastest Texture2D resize tool for Unity.
Has no limits on texture formats and works even with textures that aren't Read/Write enabled.
Inside Editor textures can be resized directly from Project window or by using batch converter with builtin Texture Converter tool.
Run-time API adds ResizePro() extension methods to the Texture2D class.
Compatible with all render pipelines.
Before purchasing, check documentation.
Asset is already included in the Amazing Tools Bundle.
Note:
Scripts are packed in dll.