system
A chat on subreddit /r/wallstreetbets
human
You're close but the point of selling a $10C and buying a $15C is so you don't have to buy at market. Each spread has a maximum loss off $500 because if the $10s are executed you also execute your $15 so you don't have to buy at market. 
  
 Basically if someone executes at 10 you have to buy at 15 and take the instant $500 hit per contract. Minus the premiums he received of course.

gpt
Ah, that makes sense. Assuming that guy did exactly that, what was the issue then? Did he lose more than the 500$ due to a margin call?