Meteor gets loaded that fast locally, because it doesn't depend on your internet connection and the files can just be read from your harddrive and don't need to be downloaded. And once the data is loaded it's the same everywhere you host, because the client (you) perform all actions on your cached mongo database and then just wait for the server to say if the action was alright or not.
But for the Heroku loading times, I have no idea, Sorry!
UPDATE: These are the long-pulls from SockJS that is used by Meteor. Normally these pulls only get Aborted on a hot code push (when a file is added/changed/removed).
Either you or Heroku seem to write or change something in the directory. Because then a hot code push may be initiated by Meteor.