If, after adding an SSH key to your Strongbox database, the database begins taking a long time to unlock, this could be because the SSH key is password protected.
Password protected SSH keys use bcrypt. This creates an additional overhead that needs to be decrypted whenever the database is unlocked. The extra layer of encryption is unnecessary/redundant because the key is already stored encrypted by Strongbox.
If you remove the passphrase protected key and replace it with a new exported unprotected key, this should make your database unlock faster.