Are you shutting down all non-essential programs before starting the game, especially anti-virus and any backup programs that may be monitoring the My Documents folder?
Firewalls have caused long save and load times, but I don't recall if that was location (or level size) dependent.
Try browsing to the '..\Documents\Larian Studios\Divinity Original Sin 2\LevelCache' folder and delete the contents. A corrupt file there can cause problems when saving or loading.
Try exiting out of the Steam client, if applicable, and starting the game directly from the '..\SteamApps\common\Divinity Original Sin 2\bin\EoCApp.exe' program file, by right clicking and running as administrator.
Try doing a clean boot and then test the game. Click Start, or hit WinKey-R, type in msconfig and hit enter; in the General tab, click Selective Startup, uncheck Load startup items (if required) and leave Load system services and Use original boot configuration options checked. Next, click on the Services tab, check the box to Hide all Microsoft services, then click the Disable All button (maybe make a note of which are currently enabled/disabled), then click OK and reboot the computer.
Run msconfig again to switch back to the normal boot configuration.