Having your printers on the netwrok automatically added can be handed on a small network, but it can become a major drag on networks with a large number of printers. The service repsonsible is named cups-browsed. Here is how you can disable this service, thereby no longer adding your printers. Printing services for manually installed printers will not be impacted.
sudo systemctl disable cups-browsed
Next, remove the printers you do not want through the printer settings applet. They will no longer be re-added.