Not OP but I found Lollipop pretty laggy and that it didn't add much I wanted, most of Google's updates come via Play now anyway. So also no reason to upgrade to Marshmallow either.
And (more relevant to the discussion), you can actually disable access to individual permissions regardless of what the app requires (though on apps compiled against older sdks there's no guarantee that they won't crash, but I found that it's not an issue in practice and most apps work just fine even if you disable access to things they supposedly require).
If you have a nexus 5 why aren't you on marshmallow?