Possible, however depends on a few factors, server upstream, game server slots, client downstream's, among other things.
Game Server: 8 Slots
Map Size: 40MB
6 people download map (if their own Internet is fast enough, they would start slowing eachother at ~16.5MBIT .. at 16.5MBIT (2MB/sec) would have 40MB done in ~20 seconds.
6 are playing, two more connect downloading at ~30MBIT (3.7MB/sec) would have the map done in ~11 seconds - with a whole 40+MBIT/sec left over for the 6 playing.
And, not everyone has that hypothetical 30+MBIT/sec