The update is still in its infant stages and is reported to be available in Cambodia, mainly through Samsung's Smart Switch PC suite. If you are feeling a bit impatient and own a Note 5 N920C, you can grab the firmware from SamMobile's page (linked below) and install it manually.
Android 6 Marshmallow brings a slew of new features, most prominently native fingerprint scanner support, Doze mode, granular app permissions, and Google Now on Tap. Samsung's updated TouchWiz will also come with an improved Internet browser with integrated ad blocking.
In all fairness, Galaxy S6 and Note 5 owners don't have that much to be excited about — TouchWiz already has fingerprint scanner support, which obviously works great, and Samsung's Smart Manager app is great at blocking battery-draining apps in the background (something that Android's new Doze mode is supposed to do). Granular app permissions (the feature where you will be able to grant and take away certain permissions in a case-by-case basis), and Google Now on Tap (contextual search, which allows you to get information about whatever you have on your screen by just holding the home button), however, are new to the Sammyverse and will add a breath of fresh air.
According to Samsung's update schedule, there are 4 more devices that need to get Marshmallow before the end of Q1 2016. These are the Galaxy S5, S5 Neo, Note 4, and Note Edge. Owners of these devices are probably a bit more excited about the upcoming update, because it seems like it will not only bring Google's new features, but also install the new and revamped TouchWiz interface on their handsets. In case you missed it – Samsung lightened its interface quite a bit in 2015, making the Galaxy S6, S6 edge, S6 edge+, and Note 5 much snappier devices than we've come to expect from Sammy's flagships. We have to say, we are really eager to find out if the same interface would get rid of the lag on the Note 4, Note Edge, and Galaxy S5. Staying tuned and at the edge of our seats!