This is neat! LowSpecGamer (via NeoGAF) used some external programs to tweak the game's files, reducing the volume and quality of the game's objects to such a ridiculously low extent that the game can run on a terrible, old laptop.
The proof? The footage captured here was taken on a terrible old laptop. Here are the specs:
CPU: Dual-core 1.7 GHz Intel Core i7-2637M
RAM: 8 GB DDR3
VIDEO: NVIDIA GeForce GT 540M
And it runs at a playable-enough 25fps. Not bad! Owners of terrible old laptops, remember: a crummy Witcher 3 is better than no Witcher 3 at all.