Hi,
Photoshop 2015 was not designed for macOS Monterey & has not been tested on the latest macOS. For compatibility info, please check: https://helpx.adobe.com/photoshop/kb/photoshop-and-macos-monterey.html
Also, the 2015 version if no longer available for download through the Creative Cloud desktop app. Please check the support policy here: https://helpx.adobe.com/support/programs/cc-support-policy.html#cci
It would be helpful if you could share your feedback regarding the latest version on our community so that our product team can look into it.
Please let us know of you have any other questions!
Regards,
Nikunj