Erase 2015 iMac for recycling

Please revisit and read > What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

Steps 2 thru 4 require an internet connection and being logged in.

Steps 6 and 7 require an internet connection and a USB keyboard and mouse if your wireless ones are unpaired.

6. Erase your Mac

1. Shut down your Mac.
2. Start up from macOS Recovery, then use Disk Utility to erase your Mac. For details, follow the steps to use Disk Utility to erase your Mac.
3. When done, quit Disk Utility but don't restart your Mac.

7. Reinstall macOS

1. While still in macOS Recovery, choose Reinstall macOS, then follow the onscreen instructions. Learn more about reinstalling macOS from macOS Recovery. 
2. After reinstalling macOS, your Mac restarts to a setup assistant. Press Command-Q to shut down instead of continuing setup.

lyndee97 wrote:

Thank you for the quick response.

You're welcome.

Is it necessary to reinstall the OS or can I stop after step 6 and shut down?

If you are just recycling, then no. If you are trading it in for a gift card, then yes.

Is there any possibility that going through these steps will in anyway affect other computers on the same network or other computers using the shared family iCloud?

Not if you follow the sign-out directions in steps 2 thru 4.

You’re welcome.