Ok, I found out what their specs are, and I would say that they (based on my naive, ignorant, uninformed little opinion) fairly overstated what you need.
I'm running Witcher 3 on a 2009 Mac Pro, running Win7 Pro, with 32GB RAM, 8-cores Xeon processor -- but I don't think that really impacts the game that much...(they usually set the RAM requirements in the code, and anything above that doesn't really impact the game...and the processor doesn't seem to be as important as the GPU, in my experience).
My GPU is a Nvidia 660 (the minimum, according to their specs), with 2GB of RAM, and I'm absolutely stunned at how beautiful the game looks and how smooth it is. I'm playing it on the default settings that it came up with, I think I just nudged up the one slider for better terrain further back, but again, I'm still in awe at how beautiful the game looks.
They say the min specs are:
Minimum system requirements - Windows:
OS: 64-bit Windows 7 or 64-bit Windows 8 (8.1)
Processor: Intel CPU Core i5-2500K 3.3 GHz or AMD CPU Phenom II X4 940
Memory: RAM 6 GB
Graphics: Nvidia GPU GeForce GTX 660 / AMD GPU Radeon HD 7870
Please mind that we only officially support full-size desktop graphics cards
Hard Drive: 35 GB of available space
DirectX: 11
Understand that mobile GPU's are really much less powerful than the real version, but if you already bought the game, go for it. If not...just wait a while for the price to come down, and give it a shot.
Thinking out loud...if I didn't have a decent GPU already, and I was going to buy one, I might consider getting a PS4...but being able to tweak more things, or access more mods really seems worth it to me.