If you haven't already you might also want to look into satellite internet service. Depending on the provider it should be a lot faster speeds then what you are currently getting.

Also if your speeds are slow you should download only one update at a time. Click on the show details option at the bottom and uncheck everything but one item. Trying to do all the updates at once on a slow internet connection is just a miserable experience and it will increase the chance of problems like you are experiencing. Also not all updates are required or necessary. For example you don't need to update Garage Band if you don't use the application.

Just doing one at a time is not great either with your current speeds so if you can find a faster internet source elsewhere as mentioned by others then that's the preferred method.