eMc v6 slow to sync emails

My v6 has been intermittently slow to sync in recent months and I think I know what’s happening after watching operations during the sync process. The headers load promptly but content can take 3-4-5 min. I have maybe 300 folders with 2/3 Local Folders. it’s trying to sync ALL these folders even though there’s nothing to sync except the IN box. I do have just one “rule” for it to deal with and dump selected email in a specific folder.

Any recommendations on how to manage folders? have more as local vs IMAP? Reduce the number of folders?  I don’ get why it’s doing anything with local folders.

Thanks in advance for any guidance.