Just as a comment to anyone who searches and finds this post. When you move a wallet.dat file from one machine or core install to another by default it is going to want to scan the entire block chain to find all the transactions that may be associated with this wallet.
On older / slower machines it will take some time.
-Dave
It would be useful if the wallet is already synced to have a switch or button in the GUI that stops the rescan. Like there is the abortrescan RPC call when you launch Bitcoin Core from the terminal.
I have not used the GUI wallet for quite some time, so I am not sure if this feature actually exists, but checking just now on Github, it appears that this feature request was
rejected for not being popular enough.