I was trying out angular 2 the other day and I faced the same issue as you do, my vendor.js was 6M and this was a simple "Hello World" app...
I've found the following post that helped a lot in understanding how we should act on this issue (for now): http://blog.mgechev.com/2016/06/26/tree-shaking-angular2-production-build-rollup-javascript/
He uses several optimizing and compression techniques (precompile,treeshake, minify, bundle and gzip) on his 1.5M app to reduce its size to just 50kb.
Check it out, hope it helps! :)
