If you swept your old seed to a new seed without writing down your new seed, you can't recover them unless you know the seed. If you know your password for your new wallet(seed), you can unlock the wallet and send all the coins to a new address with a known seed. You can also click the Backup Wallet (or somethings similar) in the ui if you know the password to unlock your wallet to get the seed of the wallet.
In my case too it takes several days to synchronize and my computer. My internet speed was not so much. It around 20 Mbps, my CPU is an i5 of only a few years old and while the consensus file is not on an SSD, it is on a speedy 7200rpm HDD. Of course, I also added extra nodes from