ng build --prod is extremely slow

Increasing node's allotted memory size really sped things up for me. You can see here I gave it an entire 8GB as opposed to the default 512MB.

> node --max_old_space_size=8192 ./node_modules/@angular/cli/bin/ng build --prod

If you are unsure of how much memory your machine has available use the following command to see memory stats based on MB, check under the available column not the free column.

> free -m
              total        used        free      shared  buff/cache   available
Mem:          15866        1490        3726         116       10650       13929