If you want to test removing parts of Kiel you guys should comma out from this file:-
C:\Ubisoft\Silent Hunter 5\data\Campaigns\CampaignProjects\Total_Germany.pj
Code:
[Layer20]
LayerType=0
MissionName=PlayerBases
[Layer21]
LayerType=0
MissionName=Harbors
Another thing you may want to test is to remove the two naval bases/ports that are within render range of Kiel
Also - try object editor to thin out the buildings etc