How to Erase All Content and Settings Macbook 2015

the first T2 chip equipped MacBook Pro models were the 2018 models, so the article you linked from does not apply. But this article does:

What to do before you sell, give away, or trade in your Mac - Apple Support

.

What is the purpose here? If you are going to give this laptop to someone else, then here is an Apple article with what you should do:

What to do before you sell, give away, or trade in your Mac - Apple Support

If the AppleID was used to purchase anything from the App Store, then those apps will cause problems for the new user as they will still be associated with your AppleID. The easiest method really is to perform a clean install of macOS as that will clean up the years of built up junk. If you insist on just keeping the Mac the way it is, then create a new admin user account for the new user, then delete your old user account. This won't affect any system wide settings, but the new user will have default settings in their user account.

Do the new user a favor and perform the clean install.