I just tested on my machine (i7-6900k, 8C/16T from 6 years ago), building 5.15: qtbase, qtdeclarative, graphicaleffects,multimedia,quick controls2, serial port, svg, wayland and websockets takes 8 minutes total... it's hardly the end of the world and that's already more than needed for 99.9% of Qt apps. And I don't even use ccache.
make -j16 5343,12s user 307,95s system 1198% cpu 7:51,67 total
Oh sure, building an isolated Qt instance is quick.
But adding the Yocto overhead (entire bootloader, kernel, and then fetch/decompress/build all the packages) takes a bit more time. And Qwebkit isn't trivial either.
Once Yocto has it all in sstate-cache then it's only like 15 minutes for a total rebuild.
