The issue sounds like the map rendering on the server as you mention but one test is to publish a very simple view with a similiar map to determine if the issue relates to the data and rendering the view which can slow if a large amount of data is in the view vs there being an issue with the maps rendering slowly over the internet.
Have you tried the Miami and Havana tile request from the server as is mentioned in the online help? is this an instantaneous response or does it take time? It should be available very quickly. This too should help pinpoint the cause of the issue.