Will Marshmallow and Doze Mode fix the battery problems Lollipop brought to the M8?

My HTC One M8 was running fine before the Lollipop update back in January. KitKat had great battery life (I had at least 30% when I got to bed) and never had lag. Since then I have to charge it a bit during the afternoon if I dont want to risk running out of battery and I have occacional lag which goes away when I clean the recent apps. Tried cache cleaning, did 2 factory resets, a couple of custom roms 5.1 based and even flashed the RUU file to bring it back to pristine state, to no avail since Android OS and Android Kernel are to 2 most battery draining app I have (checked on Gsam battery monitor). SOT is much worse also, I only get 3 - 3,5h maximum.
Do you guys believe Google and HTC are able to bring the battery life of this otherwise great smartphone to how it was before LolliFLOP?

Cheers