How high is 15% chance of pregnancy?

I'm on my 3rd day of my fertile window right now, app says.

So i had "a lot of sex" today. It was 9% chance of pregnancy few days ago.

So how high is 15% of the pregnancy chance? Haven't used any other protections except condom. But it slipped and stayed inside my vagina at the end of the sex.

Lil bit worried i might get pregnant :<

Should i get a medicine? (Also i cant quite get the explanations on the internet, which is english is not my mother language.) So its kind of a trickyto me now..

Gals, halp. :)