Docker: meteor build really slow

Within the docker ubuntu:latest image we installed meteor by calling

curl https:://install.meteor.com | sh

If we want to build a project inside this docker image it takes unusually long compared to a build done directly on the same machine outside a docker image (20-30 min vs. 2-5 min).

Because of educational purposes we don't want to switch to some other images like MUP but we need to understand how to fix the problem within the given context. We are totally without an idea how to debug this case or how to configure the container properly. Some help is highly appropriated.