Files open very slow

Thanks for getting back to me so swiftly Platinumaa.

Fixing permissions won't change anything to the permissions the app was granted upon installing; the fix within the app's preferences I mentioned above is fixing the different permissions the files within your Dropbox folder have.

Quoting from the relevant resource, this is how to install the Dropbox desktop app with admin privileges:

1. If you already have Dropbox installed, uninstall the application.
2. Download the Dropbox application.
3. Open the installer.
   • Do not right-click, and do not command-click Run as an Administrator
4. Follow the instructions in the install wizard.
   • If you’re asked for an administrative username and password, enter them or contact your administrator to sign in.
   • If you’re not asked for an administrative username and password, you’re already an admin on your computer.
5. Complete the installation and sign in to Dropbox.

And, yes, the 'Fix Permissions' and/or the 'Fix Hardlinks' buttons will force your files to sync anew when applied. 

In any case, please take as much time as you need and report back with your findings. 

Until we speak again, take care!