That's just a general assumption. If you're not checking suggestions, then there's no real way to troubleshoot for you. Sometimes you have to manually rule out things even if they seem obvious. FYI: I've exceeded 8GB usage while using FFXIV with windows 10 installed and a minimal set of apps. I'm running a 980, which your card is minus a single laser cut, and do not have these issues you speak of.

Another issue might be you allowing the creators update to install which is highly counterproductive to FFXIV performance.