When looking at all of the email templates on the Email Templates page, you can filter the page to show only your templates.
Click the filter button in the upper right corner. There are two options: My Templates and Other Templates.
If you check the checkbox next to My Templates and uncheck Other Templates, then only templates made by you will show. All templates made by other users will be hidden. Note: folders remain. So if there's a folder made by someone else containing only templates made by them, then that folder will still be shown, but it will be empty.
If you uncheck My Templates and only check Other Templates, then all templates made by you will be hidden. Again, folders remain, so the folder's you've made containing templates made by you will still be displayed, but they'll be empty.
Once you've made your selection, make sure to click the Update button to apply the filter.