SS has the right idea for stamina. Go in extra horny, tell your guy you want o get off right away, do it, start round two.
And 3-15 minutes is totally fine. It MAy be that in an actual sexual context, you reach orgasm even faster. In which case, you might try going for two rounds. Or, if you're not up for that,just focus on getting your partner excited with your mouth, hands or other body parts, until he's as horny and ready to finish as you are.
As fas as shooting oes, you can usually improve your shooting performance skightly (or somewhat, or a lot) by doing Kegel exercises. No harm in looking them up and giving them a try. That said, I doubt anyone will really care if you're a shooter or an oozer. A shooter makes for a nice visual, but it's probably pretty low on nearly every guy's list of qualifications for a sex partner.
And while we're on the subject of "practicing at home", you might also practice edging. That's getting right up to an orgasm, stopping, letting the feelings subside a bit, then starting again. It sounds a bit tortuous, but it's actually a lot of fun. Your sex drive keeps ramping up and up, and the final orgasm is often pretty spectacular.

. So edging can get you two benefits - how to back off from orgasm to prolong a sex session, and how to have a bigger orgasm.
Lex