Samsung Galaxy Android 6.0 Release Isn't Close
At this point, it looks like the Samsung Galaxy Android Marshmallow update will follow Samsung's Android 5.1.1 release. Google's promised the update for Q3 and with Q3 set to end when September ends, we should see it arrive next month.
Samsung hasn't confirmed any specific Android 6.0 release details yet and SamMobile, a trusted source, claims that Samsung hasn't even begun developing Android M for its Galaxy devices yet. This doesn't mean that the update isn't coming it just means that it could be awhile.
A Samsung Galaxy Android 6.0 release in September seems unlikely at this point though we do expect to see updates arrive sometime this year. The Galaxy S5 Lollipop update first started rolling out back in December so the door is open for an early release.