No, I did not set the password for the wallet at that time, someone else did, and not knowing the password was not as important as it is now.
So, you have no idea about possible passphrases.
Unless the passphrase is short and it contains only a few characters, there is no way to brute-force that.
Since you say the password was set by someone else, I doubt that's yours.
Isn't the wallet owned by the person who set the password?