The Cisco router must be configured to enforce a minimum 15-character password length.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. Password length is one factor of several that helps to determine strength and how long it takes to crack a password.
The shorter the password, the lower the number of possible combinations that need to be tested before the password is compromised. Use of more characters in a password helps to exponentially increase the time and/or resources required to compromise the password.