Intel® Open Image Denoise

Rendered with one sample + denoise (under a minute) on a 10 years old machine, using cpu

pngquant 4 file.png

200 samples ↓

200 samples, 15min - Real deal.

Blender 2.81 release notes
https://wiki.blender.org/wiki/Reference/Release_Notes/2.81/Cycles

How about ~2 minutes ↓

https://i.imgur.com/KFYCYPv.jpg - Blender old internal denoiser, 1 sample, 1:49
https://i.imgur.com/ePXJskx.jpg - Open image denoise, 23 samples, 2:19

Nodes ↓