by the time sony phones receives Android M update for his Z3C, he'll probably start a thread for purchasing a new phone. ( unless OP plans to root )
Thats the speed by which sony rolls out the update for its phone.
As far as Lollipop vs kitkat is concerned, I feel Lollipop gets the job done in my Yureka ( stock Rom). apart from a few minor bugs, i don't have much problems with the phone. The general consensus for Lollipop is negative though. :/