I like what this XDA user had to say about this issue.
This is Touchwiz, not the Lollipop memory bug, which has been fixed. Other lollipop based devices are not aggressively killing apps. Nexus 6 you can routinely have a good dozen or more apps in the background and they won't refresh.
Likewise even Moto X has around 8-9 and has half the ram of the Note 5 and 50% less than the S6
HTC M9 - similar story to the Nexus 6 regarding backgrounded apps
Sony Z3 - same story again.
M9 is running a heavily skinned OS and Z3 has a less heavily but still skinned take too. Yet none of these devices have ram management issues and all of them are performing better in multitasking and are running Lollipop
This is Touchwiz. What's more unfathomable is why with the Note 5 it can't run any more apps in the background than the S6/S6E despite that extra 1Gb of ram. Again it's another case of Samsungs excellent hardware and muscle power being heavily compromised by a skin that whilst given a lick of paint - is under the hood still a terrible bloated by legacy code, utter resource hog.
The disappointment is simple, imagine how fast these devices would be running a different manufacturers skin or stock. It's a shame Samsung have made no attempts here to fix this, and as they HAVE NOT ACKNOWLEDGED the Ram issue officially in any shape or form - to presume they are going to ever fix it is just wishful thinking unfortunately.