It's actually 14GiB. I'm not sure why these sites want to use GB when all our computer storage calculates in GiB (as does your internet if you have a cap).Obviously but 15 gigs for a single vid is too much for my storage and internet connection. On the bright side the vid is old and I'm pretty sure someone can compress this using new, more efficient codec without sacrificing too much quality.
Also, you're asking for 4K, 4x the number of pixels, and then asking for it to be smaller. The 1080p version is about 4x smaller and won't be a transcode which will lose quality.