extension-cli: Production build is really slow.

Describe the bug Production build of scripts is really slow without any significant reason.

To Reproduce npm run build

Expected behavior I think than production build should go faster than current speed. There is not generation of source map or anything just same compilation as development with some minification. is the minifaction the issue? When I just used webpack for compiling, the speeds were significantly faster than current time even when source maps where generated with minifcation.