Asking on IRC, it was proposed that I contact the owner of the mirror to find out what was going on. I did yesterday and here is the reply:
Hi Adam,
Many thanks for the heads up! I have restarted the synch process (it seems it was stalled for some unknown reason) and the mirror should be up to date soon!
As for the slow download speeds, I do not know of a reason for this. Are you aware that in December the mirror was moved from a server in Canada to one in The Netherlands? If not, and you are in North America, that might be part of the reason for the slow down. Still, it should go faster than that, so I am interested in hearing if it remains slow for you.
...
So it should be fine now, and I will update you as to whether the speed remains an issue here in Canada.