1/6 chance of losing a 15 IPC bomber.
5/6 chance of doing average damage of 3.5 IPC (the bomber can only hit the industrial complex if it survives the AA shot)
+35/12 IPC damage, a little less than 3 IPC damage expected
-15/6 lost bomber, or 2.5 IPC loss expected from building bombers.
For 0.5 IPC net expected gain, I would rather use the bomber to help on an attack against naval or ground forces. Say you attack a territory with some infantry, fighters, bomber; say that territory is defended with an AA gun and some numbers of infantry. You have the same probability of losing the bomber, but now with each round of combat, you inflict 2 IPC expected damage (2/3 chance of destroying an infantry worth 3 IPC). So with just two rounds of combat, you will have done more damage to units that had to spend time getting to the battle front than economic damage to units that have not yet been produced that would have to march from an industrial complex to the front.
An attack on naval forces is far more rewarding, at 5+ minimum IPCs expected per round of combat, and no chance of being shot down by an AA gun.
Of course, this assumes that there is no battleship in the naval territory, and in both cases that the defending forces would not be stronger than the attacking forces, but I think that there are enough ways to ensure attacker superority in numbers that bombers are better saved for use against other targets. (Subject to change if there’s no AA gun defending, or if superior attacking power cannot be brought to bear)