According to their FAQ's the only way to watch Ad-free content is to subscribe to TeacherTube Pro. You can find the link here.
These are obviously paid subscriptions billed monthly ($9.99), quarterly ($27.97) or yearly ($97).
I don't know of any other sites which have fewer ads, however, I hope the above info is useful.
My church was considering using right now media abut the subscriber fees are quite expensive maybe the bigger the church the more worthwhile it is. Sorry cant give you a quote they will only tell you if you want to buy from them I think. But I remember it was costly thats why we stopped after the free trial.
Yes you tube has gone downhill the ads just make it like regular tv so I dont much bother with it.
May I suggest Pandora.com if you like music. They will give you (I think) 10 hours per month of listening for free, with ads. Their pro membership, at about $5 per month and no ads, seems reasonable if you use it a lot.
I have got in the habit of watching Youtube videos in a private window with Brave browser, which blocks many ads. At the moment it seems to be accepable to Youtube for many of their videos.