If you are still on 4.4.4 and have found a way to keep the update from installing you can continue to use it that way. However, as Thom says there is not yet an upgrade to 6.0, and, when (or if) it does come, you'll not get an upgrade from 4.4.4 directly to 6.0.x. You'll have to take the intermediate update to 5.1 (I believe that there was another since then, to patch the stagefright exploits). The way that ota updates work is that they are offered to the latest release, so you'll have to take every ota until you get the one for 6.
So far there have been no non-Nexus phones that were running 5.x that have been updated to 6, so there is no way of knowing just yet if the marshmallow update is as troublesome as the first lollipop versions were last year. But a "last year" phone like the Turbo will not get marshmallow early anyway, so it's likely that any early bugs will have been squashed by the time it does.
