This is a refactoring release, and a small bugfix. If you're not familiar with refactoring, this is basically when you clean up code in a way that the system itself still works the same, but is easier for developers to maintain and extend.
Wikipedia knows more:
https://en.wikipedia.org/wiki/Code_refactoring
This release additionally fixes a bug introduced in 3.16.0 where the daily view could trigger an infinite loop. No one said you can get such a big refactoring exactly right on the first try!
To cut the story short: The system should feel exactly the same to you as 3.15.0, so there is no need to upgrade to 3.16.1. If this is the first time you install leihs, feel free to use this release.