beebiesims I would guess the issue is your 277 GB of custom content, either the total amount or one or more of your files. That's a lot of data for any computer to load even if it's only loading pointers and other small bits. One detail that may help is disabling the mods/cc pop-up at the Main Menu.
It's also very possible that you still have broken cc in your collection. There is no tool that can detect all broken cc, and no list that covers everything. So I'd suggest testing your cc in batches and seeing whether you can find a subfolder that contributes excessively to the longer loading times.