I'm having the same issue on the same software versions.
It's a large document ~130 pages with a lot of tables. Typing and scrolling are both laggy and I'm frequently getting SBBOD when I change a style (e.g. set a highlighted section of text to bold takes ~5 secs).
CPU usage is <1% when Word is in the background, but bring it to the front and CPU is >50%. It jumps to 80-110% when typing or making changes.
I have the latest Word for Windows in a VM with a fraction of the resources allocated and am not seeing the same issues with this document.
Changing to Draft view has sped up scrolling and improved typing lag somewhat, but the high CPU usage remains.
UPDATE: updating to the latest fast preview (15.31 161227) has fixed the lagginess, but still experiencing 40-50% CPU when typing. At least it's now usable.