I'm also working mission 15... some start hints on this mission
are:

Send out a scout and go north from your HQ, some place up there is
a mountain area, now go east and find the coast-line (which is in
the red area).. Between the mountains and the coast you build a
warehouse, quickly get some soldiers up there to defend it. Also
move most of your men, women and wizards up there. Build your
area around the warehouse to get access to the mountains and the
vital supplys (This is a long-play-war-level)..
- As I think you'd like to work from here, good luck -

BTW: I can tell you that where I stand now I'm in year 76 and
I've almost completed the war, so it's a long one..

Oh yes, a general hint if you don't know it, always have spare
men in your stock to do transports, else your people won't get
what they need. If you build 3 breeding-huts (Can't remember
the real name) in the beginning, you should ensure a good flow
of men, and by using the materials for the huts you delay some
of your building plans a bit..  It's perfectly possible to
build large populations without fish, meat, wine and bread, you
can run streight on Vegetables, Fruit and Water. But make sure
you got enough of that...