As far as I know, yes - ever since the actual network process of hosting was taken over by Blizzard servers, when a map that is not yet in Blizzard's database is hosted, the map's data needs to be uploaded from the person who created the lobby's computer to the Blizzard database in order for it to then be downloaded by people joining the lobby.
Depending on the lobby creator's upload speed (often slower than one's download speed), it could take a bit for the map data to get from their computer to the Blizzard Server in order to then be available for download by people who join the lobby.
As an example, my Internet connection has around a 200 Megabit (25 Megabyte) per second download speed, but a mere 6 or so Megabit (less than one Megabyte) per second upload speed last time I checked on an internet speed test website.
Using those metrics, I can download a 250 MB Map in 10 seconds, but it's going to take a few minutes to upload a map not in Blizzard's database.
One work around for this is to host a private lobby, leave it empty while the map uploads, then later host publicly once it's good to go.
The only caveat is I don't believe there is a progress indicator for the upload process, so you kind of have to guess.