Information
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 needs 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.
Solution
Go to Device >> Setup >> Management.
In the 'Minimum Password Complexity' window, select the 'Edit' icon (the gear symbol in the upper-right corner of the pane).
In the 'Minimum Length' field, enter '15'.
Check the 'Enabled' box, then select 'OK'.
Commit changes by selecting 'Commit' in the upper-right corner of the screen.
Select 'OK' when the confirmation dialog appears.