[on_and_off]

The revamped permission model is enough to make the update worth it IMO and that's not something that can be done via an app update.

[on_and_off]

Also, ART (the new vm introduced in Lollipop) was still pretty rough in Lollipop.

IIRC it even has some memory leaks ...

It is MUCH better in Marshmallow, so it is definitely worth upgrading because that's another thing where you just need to update the system.