I wonder...
If you could manage 2 days off a nexus on marshmallow, I wonder how long you'll manage on a phone which comes with power saving baked in a selling point? (I'm thinking the sony Xperias here).
It's always worth noting what Google gets upto with the nexus line but only as a guide to what's coming to others manufacturers later on (though if you want the bleeding edge of Android software that's your choice to make by buying a nexus. I'm not saying it's not a valid choice, it's just not one I personally make).