It's possible is slower than normal today, since we just had an update and many people are surely running it. If you have the most current Addon Manager, it uses two mirrors, and the one used is chosen at random at every start, just to do a bit of load balancing between users.
If downloaded before yesterday, the update will still work normally, but the installer used only one server, so that one might be slower if many users are still using that version, but it will probably become faster after this update, both because there's now load balancing between servers with the new installer, and because now every file is first checked for having updated on the server before being downloaded, this should make future Updates faster.
