Hmm 2,5GB seems to be good so far. It is a 4k video around 40min long. If you would like to watch on Librem 5 (720p), you would need 9 times less data. So you would have to download just less then 300MB. That is a common value.
If I record something in non-compressed 4k *.avi video format, it can take over 1GB in 10 seconds. Just to compare how much data is already compressed in this 40min video. A whole series at this compression rate in 720p and 25min x 12 videos would take 2,1GB.
The other question is: is it necessary to see his face in 4k? He also could upload this video in 720p and we wouldn’t miss any important detail. 