In many places, 18+ porn comics are considered illegal. This is because they can have a negative impact on society and violate moral and legal standards.
I have no idea. There's no obvious or common link between 7 15 and X-Men comics. Maybe it's a code or reference within a very niche aspect of X-Men lore that isn't widely known.
The X-Men Black comic was indeed cancelled. It could be due to a combination of factors such as changes in the comic market, reader preferences, or editorial directions within the publishing house.