I agree with everything Andrew has said. From a personal perspective, when I changed from having Office and my documents on a (relatively fast) HDD to an SSD, the speed and responsiveness change was quite noticeable.
I still store the bulk of my documents on the HDD drive though. I do not know that a faster SSD would be noticeable, at all.

That is a tremendous number of section breaks. I am not saying you do not need them, only that I suspect that may be the primary problem.
When to use Section breaks in Microsoft Word (and when to not use Section Breaks)
Section breaks carry a tremendous amount of formatting information. You can reduce slow-down from them, as Andrew suggested, by working in draft view.