You can get to this area by going to Tools | Options | Text Editor | All Languages | Scroll Bars
To see a preview of code using the scroll bar change the behavior from “Use bar mode for vertical scroll bar” to “Use map mode for vertical scroll bar”
In map mode, the scrollbar shows thumbnails of the code, and if you hover over the a portion of the scrollbar, you see a preview of the code at that location.
You can control the width of the scrollbar in map mode by changing the Source Overview in the scroll bar settings. Turning off the Show Preview Tooltip setting would turn off the code preview that appears when you hover over the scrollbar.