Several years ago, when I was watching a show, it was 15:45 and the show started at 16:00. A foreigner asked me: "When will this show start?"
My English is not good, and I never talked to foreigners. I was very nervous then. I told him: "15 minutes later", but he seemed to not understand. So I thought it wasn't correct, and told him: "in 15 minutes". This time he understood.
I want to know if "in 15 minutes" is correct and "15 minutes later" is wrong under that condition? What's the difference between them?