It's a bit too easy to blame Google. The Note 4 lollipop update made my note 4 noticeably less efficient; even my Galaxy Alpha which ran at around 800mb system on KitKat jumped upto 1.3-1.4gb system on Lollipop, resulting in app refreshes and lag that were simply never there on KitKat.
Whilst it would be easy to blame Lollipop, the reality is other manufacturers have managed to embrace lollipop without such issues.
LG, HTC, Sony, Motorola devices haven't had such noticeable issues since pushing out lollipop as much as Samsung, likewise they haven't seen such massive system ram usage increase either. Now of course I'm not saying they haven't had some bugs / but nothing quite as impactful as on Samsung devices.
Samsung devices across the board are suffering noticeable poorer battery and standby ram increase across all of their devices I have had and used with it. (Note 4, Alpha, S6 Edge owned and S5, A5 used since lollipop). So there is definitely something not right with their touchwiz build on lollipop across the board.
Even the S6 with 'less bloat' uses more system ram standing still than other Samsung devices - especially under Kit Kat.
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My Note 5 dream / hopes therefore are less about hardware and more about software.
I wish Samsung would truly go back to the scratch and rebuild Touchwiz from the ground up. HTC / SONY devices have just as many features / bells and whistles and don't use anything like as much resources standing still. That speaks volumes.
I can only drool at how amazing performance on the S6 / S6 Edge would have been had they really had an optimised OS. The octo-core exynos & DDR 4 with a device with stock android level of ram usage (and you don't have to sacrifice features to get this as the M8 & M9 prove) would make an amazing combination.