A wallet with 10k addresses will poll the history of all those 10k addresses to the server.
Electrum is not optimized to handle wallets of this size for now...

If you have only a few addresses that received coins, you can try this:
- Open your wallet file (look in c:\users\myuser\appdata\roaming\electrum\wallets on windows)
- Look up the private key for the addresses that have coins
Now either
- Import these private keys in a new normal electrum wallet and send the coins somewhere.
Or
- Make a custom transaction with csv file to send the coins to a single address.
Or
- Import them in a wallets such as blockchain.info ...