It is normal. Initial checkout is about 1.1~1.3g. 68Kib is kinda slow. The git checkout contains an entire linux distro in binary form + the package management components to recompile any part as necessary.
For some reason it starts at full speed, as far as the local connection goes, and then it goes down. It may be my ISP.
But been mobile today, so I started the clone three times in different places and it goes down consistently after 50%. Maybe github is rate-limiting?
Back home, will leave all night if needed, so fourth time is the charm!