I'm not surprised you blacked out if in your first time drinking you had 15 shots of vodka.
15 shots, even in the least generous bar measure, is more than half a normal sized bottle.
If you were pouring the shots yourself, though, no doubt you poured yourself generous doubles, so it was probably more than a full bottle that you drank. That's not a safe amount for anyone to drink, ever, in a single session - let alone someone who's never had alcohol before.
My advice, stick to beer until you know you can handle spirits and even then, be more moderate about what you drink and don't drink a whole bottle in a single sesh. Also, it's fine not to drink, and you should never feel pressured into drinking if you don't really want to.