Remove icons and non required fonts

Ionic Framework ionic-v3
4

Take a look at: GitHub - ionic-team/ionic-app-scripts: App Build Scripts for Ionic Projects

And, create your own copy.config.js:

module.exports = {
  copyAssets: {
    src: ['{{SRC}}/assets/**/*'],
    dest: '{{WWW}}/assets'
  },
  copyIndexContent: {
    src: ['{{SRC}}/index.html', '{{SRC}}/manifest.json'],
    dest: '{{WWW}}'
  },
  copyFonts: {
    src: ['{{ROOT}}/node_modules/ionic-angular/fonts/noto-sans**',
          '{{ROOT}}/node_modules/ionic-angular/fonts/roboto**'],
    dest: '{{WWW}}/assets/fonts'
  },
  copyPolyfills: {
    src: [`{{ROOT}}/node_modules/ionic-angular/polyfills/${process.env.IONIC_POLYFILL_FILE_NAME}`],
    dest: '{{BUILD}}'
  },
  copySwToolbox: {
    src: ['{{ROOT}}/node_modules/sw-toolbox/sw-toolbox.js'],
    dest: '{{BUILD}}'
  }
};

See: https://robferguson.org/blog/2018/04/17/optimising-the-performance-of-an-ionic-pwa-part-2/