As Roland said, there is no need to load the entire namespace, which is the reason your bundle size is so big.
load the specific files from their specific directories (and not directly from the main directory @babylonjs/core alone), and make sure not to use the legacy endpoint, which is mainly used in the UMD package.
The babylon package includes unminified code for your convenience, as a final step for production release I would recommend you to minify your code (using a bundler will help here)