When scheduling your template to a group, the drop-down list will show all the groups you are admin. of, in alphabetical order (including if emojis are used at the beginning of the name of the group, those will appear lower on the list).
Our engineers are always working on solutions to improve the program, but currently, the only way to shorten that list is to:
Delete the group directly on FB (by removing all members including yourself last. Archiving won't be enough),
Remove yourself as admin of those groups,
TIP: It might be easier to rename some groups so they appear at the bottom of the alphabetical list. Adding an emoji right at the front of the group name, will bump it to the bottom of the list.