Good news! I’m very happy to report that this issue was resolved for me by following some advice I found on a youtube video.
In short, the video says to hold the shift key while clicking on preferences. Go to the tab called “Internal.” Search for “so4”. There will be four options listed. Switch the one that says it is a “compound reader” to FALSE.
Apparently this compound reader is only important for 10-bit video files created by specific phones and DSLR cameras, so most people don’t need it and it resolves a lot of crashing.
The video was for Vegas Pro 17, but I’m using Vegas Pro 15, and this solution worked for me! After three hours of reading forums, trying things, restarting my computer, and nothing else working, this little “fix” worked! Yey!!!