The reason for this long times is that the received URL is a compact view of the full kie workbench (EmbeddedFormDisplayView). This view is loading the full errai framework and lots of things.
We have the same problem and have reduced a little the time erasing the contents of the plugins folder inside war content, but it is still tooooo slow.
We are still investigating other ways to improve this poor load time.
The simples way could be reusing this embeded view across multiple usages, but it requires changed inside GWT stuff we are not thinking on them, yet.