The 15Base mission is the defender version of base assault.
Unfortunately there seems to be a bug in the script, as I've never seen the mission actually get offered in a campaign.
Usually that comes about because of one of
- a flaw in the message text
- a flaw in the mission maps
- a flaw in the team selection/drafting setup
I keep meaning to go over the script in detail to see if I can spot the problem,
but haven't done so to date. One fine day
As for eliminating the AI interaction, usually I just set the AI population controls to something ridiculously low in the MetaMap.gf file. E.g. variables TargetPopulationToEconomicRatio, InitalAILevel, and MaxAIsPerEmpire. Dunno if BB does something similar or not.
dave
PS - I did confirm a couple of glitches from the pirate-player perspective for the OP versions, see the edited post up top