An adventurous person might do it. They love to take risks and seek challenges, and climbing 15 stories is definitely a huge challenge.
A person who is very determined and has a strong will. Climbing that many stories is not easy. It requires a lot of perseverance. He might be someone who has set a goal for himself, like proving that he can overcome great heights, and he won't stop until he reaches the top of those 15 stories.
Maybe he was trying to escape from something, like a fire or a dangerous situation in the building. He might have thought climbing was the only way out.
It could be that he is in an emergency situation. For example, there was a fire in the building and the stairs were blocked, so he had no choice but to climb the outside of the building. And he might have some basic climbing knowledge and enough courage to attempt this dangerous climb of 15 stories.
If he was climbing for a legitimate reason, like a rescue operation or if he had prior permission from the building owner, then it could be legal. But just randomly climbing 15 stories of a building in Philadelphia without any authorization is likely against the law.
He might have used the external structures of the building, like window ledges and drainpipes, to pull himself up.
It could be that the elevators are out of order and he's in a hurry to get out of the building, so he chooses to climb down 15 stories. There might be an important meeting or appointment he doesn't want to be late for. Also, perhaps he just wants some adventure or a physical challenge, although climbing down 15 stories is quite a risky adventure. He might be a thrill - seeker who likes to do extreme things.
As a fan of online literature, I don't judge or comment on the real world. However, in real life, everyone had their own advantages and limitations, and they could not completely avoid any problems or challenges. Some men may be unable to accomplish certain things in certain situations, but that doesn't mean they don't exist.
He could be doing it for a bet. Perhaps he wagered with his friends that he could climb that many stories.
It could be a dare or a part of some extreme fitness challenge he set for himself. Some people like to push their physical limits in unique ways, and climbing 15 stories is no easy feat. It might be his way of proving his strength and endurance to himself or others.
Maybe he is trying to get a better view of Paris from a higher place.
He might be sweaty and a bit out of breath from the climb.