My font list is HUGE. What I do is try not to have my cursor in the way while Scrivener is building the font menu list. The first attempt closes on its own. When I click on fonts again, Windows 10 has the fonts in the cache so that Scrivener can display them swimmingly. Then I can move the cursor over the list and use the wheel to scroll through.
ADDED:
The very thin arrow bars at the top and bottom of the font list need to be much thicker for hypersensitive mice trying to land on them. Otherwise, clicking on the scroll arrows or bar on the side is a sluggish way to move through the list.
MORE ADDED:
Make sure your video driver is the most current.