Alright but... Wasnt the Hanse at the heigh of its power in 15th century, i know the whole hanse cant be united but couldnt, Mecklendberg,Luubek, Hamburg, pommerania all unite, after all arent they within close proximity to each other. We could see a potential baltic power, also maybe Bremen unites, I can see this happening if the Hanse states start to fear the growing power of the Habsburgs and because denmark has the sound toll, the leasers can see that if they united then they may have a chance to defeat Denmark. So i see it as plausable.
Thoughts??
As I said the problem is their short-sightedness. At least seen from today.

(Just to give an example. In the 16th century Luebeck did built dedicated warships during the war with Sweden. The "Adler von Lübeck" at that time was the largest warship in Europe (in the world?). After the peace treaty 1570 it was converted into a cargo ship.
http://en.wikipedia.org/wiki/Adler_von_Lübeck)
Combining some rich prosperous Hanse towns with the 2 duchies of Mecklenburg and Pommerania, maybe Saxe-Lauenburg too, would have given them a continuous border plus some manpower to defend it. Not sure if it would have been enough in the coming centuries though.
Problem is that each Hanse town was fiercely defending its own independence. Well, maybe more the already rich merchant families in the town councils were doing that.
And they were quite suspicious of the rulers close to them. Maybe not without reason. I´m quite sure that a Duke of Mecklenburg or Pommerania would have loved to gain possession of a prosperous (Hanse) Baltic port town.
In our time line they didn´t even unite - although they were all Protestant - to defend themselves together in the 30 year war.
It is true that Hamburg was never attacked or besieged in that war. But that happened because Hamburg just spend a lot of money to modernize its fortifications. Starting around 1600 if I remember correctly.
And that was against a perceived Danish threat when the work started.
You would need something truly shocking happening. Something that convinced at least some of them that close cooperation was needed for their survival. Which might then develop over time into a closer federation.
Another problem is geography.
Most similar to your envisioned Baltic power would be the Netherlands?
A relatively small coastal country relying on trade.
The Netherlands though mostly had to defend against one enemy, Habsburg Spain. They could normally count on the neutrality or even help from France or England, both enemies of Spain too. And didn´t face a threat from Northern Germany in the east.
The Hanse Baltic power probably would face several enemies. Denmark for sure would´t like it. Same with Sweden later on. Or Brandenburg in the south. Or the Polish-Lithuanian Commonwealth in the east?
I realize most of them don´t yet exist (or aren´t threats) in the 15th century.
But sooner or later you´d need a "great power" close by support you.
The Dutch had the advantage that once they were independent no great power around them was willing to see them conquered by one of their competitors. Seems to me the situation for the Hanse Baltic state would be slightly different. Quite a lot of countries and German principalities would gain something by dividing them up among themselves.