The number 15 in a dream represents facing change. Living with the consequences of a change that has occurred in your life that you couldn't stop.
In a positive sense it points to problems that go away on their own or good things that begin to happen with no effort. Feeling good about bad people finally deserving to stop doing something you don't like. Vain people facing their karma. Changes that erase vanity.
Negatively, 15 points to living with problems you didn't want to deal with. Often pointing to arrogance that embarrasses you or a loss of status or power. Confronting your own vanity or ego in unpleasant challenges. Becoming a complete loser after first having showed off that you are perfect winner. Feeling forced to make concessions to people you've never had to make them to previously. Making small changes in order to keep arrogant leverage over people who are trying to escape it. Awareness of yourself becoming a total snob to people who were previously more powerful than you.
Confronting your enemy who has become so vain that they want to enjoy watching you becoming a total loser. Confronting people who are starting to reveal their true character that wants to enjoy being better than you before all else. Confronting the truth of why people are fake. Confronting jealousy in others that doesn't like you if you are better than they are in any way at all. People who enjoy thinking they are better looking than you are to your face. Ignorant competition to be better than other people. Feeling kept down in life or competed with by vain people who are jealous of you getting bigger than them. Confidence in being right with enemies who will risk everything to destroy you anyway.
Ignorant vain homosexual jealousy. Ignorant petty jealousy. Ignorant wimps losing power that will resort to childish behavior to stop you from achieving bigger power than them.
Example: A man dreamed of seeing the number 15. In waking life he was having weird feelings about experiencing President Barack Obama starting to remove the embargo on Cuba. He felt the embargo was totally arrogant and that the US was only changing it's stance on Cuba because they felt forced to make a concession to attack Russia who is Cuba's ally. In this case the number 15 may have reflected the man's feelings about America confronting it's past arrogance because it had no choice.
Example 2: A young man dreamed of seeing the number 15. In waking life he had been the smartest kid in school in grade 9. In grade 10 he got an award and had to endure all his classmates making fun of him for being the smartest person in his grade.