First, are you using Polymer 1.0? It's much lighter weight than Polymer 0.5. Second, is this a big project with lots of transitively dependencies? Like ES6 mod

First, are you using Polymer 1.0? It's much lighter weight than Polymer 0.5. Second, is this a big project with lots of transitively dependencies? Like ES6 modules, HTML imports encourages more granular files that can be referenced and loaded individually. With HTTP/1 this can cause slowdowns as you hit the browser's request limit. HTTP/2 loads a bunch of small files significantly faster. For production we recommend the `vulcanize` tool which concatenates all HTML imports into one file for fast loading. If you are using 1.0, do you have an example that shows the 2 second freeze? That shouldn't be happening.