Another possibility is that he was in a desperate situation where he thought climbing up was the only option. Maybe he was locked out of the building in an emergency and climbing up was the quickest way to get to safety or to get someone's attention on the upper floors.
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.
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 could be doing it for a bet. Perhaps he wagered with his friends that he could climb that many stories.
He might have used the external structures of the building, like window ledges and drainpipes, to pull himself up.
Maybe he is trying to get a better view of Paris from a higher place.
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 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.
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.
It could be revenge. Maybe the woman did something that made the man angry in the past, and he's taking out his rage in this extreme way.
The masked man might kidnap Lucas for ransom. Maybe Lucas comes from a wealthy family in the fanfiction world, and the kidnapper sees an opportunity to get a large sum of money.
It could be revenge-driven. Maybe he felt wronged by 99 people and took extreme action.