By default, in its latest release, Linux Mint 17.3 (Rosa) offers to switch the software repositories to a local mirror because “Local mirrors are usually faster than packages.linuxmint.com”. Unfortunately, for me, this is not the case.
The local mirror is at a university, and this institution obviously has more need for its bandwidth than supporting Linux updates. Consequently, the local mirror is actually considerably slower than the regular repositories.
But, Mint blithely continues to ask me “Do you want to switch to a local mirror?” The answer is clearly no, but this option isn’t evident in the Update Manager window.
The trick is to navigate to Edit – Preferences – Options and check the box labelled “Don’t suggest to switch to a local mirror”.