The "Karma" badges were created in order to somewhat migrate the user's karma count when the forum was migrated from the SMF framework to Discourse forum framework in 2021.
A "Karma" badge was awarded to each migrated user based on their karma count in the SMF database. I believe your persistent "Karma: 1500+" badge is the one you were awarded at that time.
"Karma" badges are also automatically awarded based on the number of 
s you have received (the system was introduced by the Discourse framework). Those badges are replaced as you are awarded each higher badge. The count is the reason for your "Karma: 3000+" badge