lock screens - Why, and how to increase 16-character lockscreen password limit?

This is a problem that has annoyed me, as the password that I have memorized is around the 20-character mark, yet Android limits it to 16 characters

Why, and how to increase, 16-character lockscreen password limit?

If it's relevant, the Android is running on 5.1 Lollipop.

Answer

From Android Security Internals: An In-Depth Guide to Android's Security :

Android doesn’t have a dedicated setting to manage the encryption pass- word after the device is encrypted, and changing the screen lock password or PIN will also silently change the device encryption password. This is most probably a usability-driven decision: most users would be confused by having to remember and enter two different passwords at different times and would probably quickly forget the less frequently used, and possibly more complex, disk encryption password. While this design is good for usability, it effectively forces users to use a simple disk encryption password, because they have to enter it each time they unlock the device, usually dozens of times a day. No one wants to enter a complex password that many times, and thus most users opt for a simple numeric PIN (unless a device policy requires otherwise)

Additionally, passwords are limited to 16 characters (a limit that is hardwired in the framework and not configurable), so using a passphrase is not an option

(Emphasis supplied)

I don't know more about this limitation and would be glad if somebody can amplify (Edit: Andrew T has clarified here to an extent)

So, that rules out increasing password length to beyond 16 ( how to increase, Androids 16 character lockscreen password limit )

Since you are on Lollipop , you may like to related pitfall (claimed to be fixed) of long passwords here Android lockscreen can be bypassed by overloading with massive password

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