Those are not Core entries so far as I know. That means that a plugin or a theme has inserted them. Since I don’t know which plugin or theme it is, or whether you are still using that plugin/theme, I can’t say whether you should delete the entries. If you are still using the plugin or theme you would probably break something.
Whether or not this will slow down your site also depends on the plugin or theme that created the entries and on how those fields are used, in particular on how they are retrieved. I general you can have thousands and thousands of entries and not notice a performance hit, but there are some uses that would severely impede MySQL performance. I don’t know if any of those apply.
Finally, this is a guess but what that looks like to me is a poorly considered mechanism for providing default values for certain keys. There are better ways to provide default in formation that pre-populating the database like that… but that is a guess. Without know the knowing the details I can’t be sure.
You are going to have to try to find what is inserting those fields. If you have shell access to the server, and it is a *nix server (Linux, BSD, or Unix proper), use grep and look for those keys. Hopefully they are hard-coded. id_field looks distinct-ish (filter will get hundreds of results) so cd to wp-content/plugins and try — grep -Rni --exclude="*.css" --exclude="*.js" "id_field" ./