UPDATE 1:

Hard coded Ivy entry points have been Removed from the angular build if you are using latest, it was previously & wrongly hardcoded inside Angular init TS github code link

Now/latest you can just do

ngcc --properties es2015 browser module main

For older versions only, please see Update 1 for newer versions

ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points

Or as par of you build inside package.json

{  
  "scripts": {    
    "postinstall": "ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points"
  }
}

Some ref configure Travis to

# custom caching for .travis.yml
install:
- npm ci
# keep the npm cache around to speed up installs
cache:
  directories:
  - "$HOME/.npm"
# you can add other 

Option 2: Much faster with yarn or pnpm

pnpm install
// or
yarn install
// or
npm install --prefer-offline --no-audit

Retain package-lock.json and folder node_modules/ between each runs. I hope you are NOT running build on brand new image every time.

If package.json or package-lock.json gets updated in next CI build, only the updated ones will be pre-processed and installed. Others will not be installed again and again.

There are various do's and dont's guidelines around package-lock.json and node_modules folder. You will find a lot to read about it on the internet and I am not going to get involved

Thumb rule: Keep package-lock.json and node_modules together

Basically a package gets installed (mentioned in package.json) if

1. There is no entry in package-lock.json
2. Updated version is available than the one entered into package-lock.json
3. Package will be removed if its not referred any more

In short, you can't do that. Current version of ngcc doesn't check for any changes and always recompile all packages upon calling ngcc command. This case can be resolved in future with angular linker but it's not certain, for sure it will improve build times.