Hmmm.  I've never seen this.  I run mirrors of very large websites and often it
takes only a couple of minutes to mirror several MBs of data.  True, it can
slow down a lot if I use a  crappy or busy proxy, but when run without a proxy
I've never had to wait long.

I run a couple of mirrors, each 3 to 8 MB, every week.  More rarely I run
mirrors that my go into the GB range, but I've never seen what you mention. 
I'd be curious to see the command line....

My condolences to you.