How long the video takes to upload is a function of your ISP's broadband upload speeds. That's not going to change regardless of Youtube vs wetransfer.
You can compress the video files before sending to make them smaller using video compression software. (I don't know what is the best / free.) Another option is to copy them to another computer that has faster internet. Or copy them to a CD and ship it to the potential buyer.
Generally 4G cell services have the fastest upload speeds available with higher-end land-based cable ISP plans being the next best option. If you have some sort of economy ISP or cell service that you're trying to use the upload speeds will be very slow.
I generally try to upload to Youtube using my cell's 4G. It is blazingly fast, almost as fast as cable download speeds. I can send a movie in 5 minutes on my cell's 4G that would take 30 minutes using Mediacom. Even if the videos are on my PC I will tether my cell phone to the PC to use Verizon's 4G instead of Mediacom.