Try, when you’re not running LR, deleting your previews folder, in case it is corrupted. The LR previews are stored in a FOLDER called catalog-name Previews.lrdata. You can just delete the entire folder. DON’T DELETE the .LRCAT file which is your LR catalog.
I don't want to delete anything yet. Why would all of my previews be corrupted? Is there any other answer as to why optimizing is taking FOREVER?