Released as part of the 15.3(3)J train, version is often considered a "stable anchor" release for sites running older hardware that cannot yet move to newer Wave 2 or Wi-Fi 6 standards.
If you are converting from a Lightweight image to this Autonomous one, you typically use the ROMMON recovery method or the CLI: Cisco Community Preparation : Set up a TFTP server on your laptop and place the file in the root directory. CLI Command Ap3g2-k9w7-tar.153-3.jf15.tar