If you only sync these five folders and ignore the rest, and that rest comprises a lot of folders and files, then I think it will be more efficient to just add those five folders to Syncthing separately and not deal with ignore patterns at all. This is because ignored files are still included in the database (see https://forum.syncthing.net/t/solved-large-index-size-with-nothing-synced-but-a-lot-of-ignores/14284), and the larger the database, the slower accessing it will be, which may have some impact here, especially considering that the hardware is weak.