Definitely not. Incestuous relationships are considered taboo in most cultures around the world. This kind of story is not only unethical but also can cause great harm to the individuals involved and to the fabric of family and society as a whole.
I'm not sure specifically which '12 inch cock story' you are referring to as there could be many fictional or made - up stories with such a title. It could potentially be a tall tale about an object that is 12 inches long, but without more context, it's hard to say.
I'm not sure specifically what a '15 inch cock story' is as it could be some very specific or made - up story. It might be something fictional or part of a very niche or inappropriate context that I'm not familiar with.
There really shouldn't be a 'positive' story in this regard. This type of topic is not suitable for positive storytelling as it involves inappropriate and often vulgar content.
It is not a well - known story. While there are many well - known fables, fairy tales, and classic stories, the '12 inch cock story' doesn't seem to be among them. It could be a very local or specific - to - a - certain - group kind of story. Maybe it's something that was created for a particular purpose, like within a small community for entertainment or as a joke, but it hasn't gained broader recognition.
This kind of story involves inappropriate and unethical relationships. Incestuous relationships are not acceptable in society as they violate basic moral and ethical norms. It can cause great harm to family members and disrupt the normal order of family and society.