Probably depends on a lot of settings. I think we use 720p 50fps at 3 or 3,5 mbps and never reach 10 gb for a football match of 2 hours when we use 4G (we have a 30 gb limit per month and I used it for 3 matches last month with no problem). And we are very happy with the quality of the video. So I think you can get away with way less than 15 gb for 2 hours if you play around with the settings.

No, we don't use Youtube. We are actually streaming to an actual tv channel (and their online service too). In vMix I use FFMPEG, but not sure if it's any difference when it comes to data size. We only use one 4G connection. We had another provider before, but the speed they gave was so bad in most places and after switching to another operator which works well all over Sweden we're very happy with the way things has been working with 4G.

Our setup is very simple with a laptop and one camera with a mixer for the audio. Mostly due to the fact that many times I am the only person who operates both the camera and all the production, but it works ok for football matches.

in case you dont trust the internet connection, and there is no real live interaction during the stream, you could consider near real time broadcast. just stop start the recording and upload the file to youtube and publish in a playlist. this way you know exactly what you upload and what you use. you can tidy up the file to upload to only real content etc. all parts together in the playlist is the complete broadcast.

if you do that every 30 minutes or so or in between sections ( songs, performance etc) the online community can watch near real time and watch from the start!

just make an intranet connection with the shared vmix recording directory and copy the generated file to a publishing computer (laptop) and upload to youtube via 4g or whatever available ( not the file being recorded of course!)

i know it's not as trendy as live, but it will generate much more audience and provide more of a watch from the start on demand service. you can also edit recorded files and provide more tailormade content while the show is going on...

in my experience livestreaming is overrated. near live is more reliable and more user friendly, higher quality upload and viewing etc, but you need to prepare some things in advance ( like setting up a playlist and promote this, and give updates of uploaded content to your followers, by email, facebook, twitter etc etc.). i find it frustrating watching a livestream but missing the start. or being unable to review a certain part right away.

anyway, that's my 5 cents.
stefan