The reason for the 15% is that FlyBe can't afford / will not pay BA for BACON, therefore they have taken a share in FlyBe that will be redeamed when FlyBe goes on the stock market next year. Give now and get paid later when it is worth something.
FlyBe have gained several hundred flight deck crew, many rated on the Dash, all of BACONs routes and slots. All the BACON aircraft will go, but at who's expence? Kind of solves your crewing problems in one go.
What does BA get? Disposes of BACON and actually gets paid for it, looks good for BA's shareholders