board manager download extremely slow

Hi, when I install or upgrade the board definitions for the ESP8266 family the download of the ~30MB takes about one hour! That happend a week ago while upgrading my board definitions and yesterday the same while installing a friends system.
How can it be so slow? Is there a way to install this without the integrated board manager and its download function? I assume the download is from github. I would guess, when I download something from there using a browser the download would be finished within seconds.

The ESP boards are NOT held on arduino servers but a private server not operated by Arduino.
They are a seperate entity and the site that holds them is subject to the vagaries of the internet.

Some slowness may also be down to individual computers and the security used on those computers.
Anti virus and similar software may benefit from being disabled during the update.