how can i down load this version to my macbook

A 2015 MacBook Pro can be upgraded to the latest version of Monterey macOS 12. See: How to download and install macOS - Apple Support

Be aware that if you upgrade to Catalina 10.15 or later you will also need to update any non-Apple 32-bit apps. See: https://www.macworld.com/article/232735/how-to-check-if-mac-software-is-32-or-64-bit.html

You can upgrade to Monterey. Get it here: How to download and install macOS - Apple Support

There were only mid-2015 MacBook Pro models, but at any rate, if you are still running macOS Mojave (10.14.6) or earlier, you may have 32-bit applications (or 64-bit applications with 32-bit dependencies) that are not supported on macOS Monterey.

I recommend that you download and run the free Go64 application to determine 32-bit application dependencies before the upgrade. If vendor available, these applications must be upgraded to their 64-bit versions before the operating system upgrade. The exception to the application upgrade process is that Microsoft 365/Office 2021 for Mac require macOS Big Sur (11.*) or later for installation.

Do not upgrade to Monterey without a last Time Machine backup either. Then don't let Monterey's Time Machine backup to that drive. Start a new Time Machine drive.

VikingOSX wrote:

There were only mid-2015 MacBook Pro models…

Indeed.