You can greatly reduce the size of your PNGs by reducing the number of colors. Some of your icons or illustrations may actually use only a few colors.

Here are the tools (thanks to Gary for the tip) that I’m using to optimize images:

ImageAlpha – https://pngmini.com/

ImageOptim – https://imageoptim.com/mac

SVGOMG – https://jakearchibald.github.io/svgomg/