Actually, if bitcoin becomes 15k then you don't have to pay anything. The put option gives you the "option" to sell a bitcoin for 10k (in this example), but you

Actually, if bitcoin becomes 15k then you don't have to pay anything. The put option gives you the "option" to sell a bitcoin for 10k (in this example), but you're not required to do so. In practice you only sell it if you'll make a profit. So in the case where bitcoin is 15k after 5 years your put option is worthless and you've just lost whatever the put option cost when you bought it.