You have nothing? No plot? No characters? No setting?
Alright, in 15 minutes you can only set up 3 characters. Setting needs to be able to be expositioned, more or less, in two sentences (plus visual cues, like costuming.) Plot can be structured into three parts 3-7 minutes long: the setup (where you present the central conflict and its history), the turning (where you hint at how the conflict will go and build emotional tension) and the ending (which is where you resolve the conflict.) Of course you know all this, so... um... yeah. There you go.
Let's try to come up with something with a happy ending, here, because I spit in the face of true art.
Setting: Somewhere duels were regularly fought. 17-18th centuries Europe would work. (Costuming would be relatively easy for these times, too.)
Characters: The Duelist (Male lead: calm and calculating always, likes Rose); Henry (Duelist's foil: passionate with no skill in arms, perhaps aspiring lawyer, loves Rose); Rose (Romantic interest, loves Henry, very witty, has a good friendship w/UST w/Duelist)
Plot summary: Begins in media res, hilltop at dawn-ish. Duelist and Henry stand in a field of roses, wearing simple clothing, armed with knives. A referee or official is nearby. Some voice over opening philosophy, maybe, from Duelist.
Flashback to earlier times. We get a day or two in the life of Duelist. He claims that the only way for him to make money is by being a fighter, as he has no other marketable skills. Since it's peacetime, that means he duels in place of the wealthy or disabled, for money. (Note: this happened historically! Weird, huh?) He lives a very frugal life, in a small, dirty house. He has a tolerable relationship to Henry--some business stuff, perhaps, which shouldn't be out of the question--dueling laws were notoriously byzantine. Goes out of his way to talk to Rose, who disapproves of his lifestyle and lets him know it, but is willing to talk. At some point she says the line "I could never love someone with blood on his hands," possibly when talking about Henry.
At one point, Duelist's UST shows, and he corners Rose in a somewhat sensuous position. She protests, but not too loudly. Henry catches them, blames Duelist, and challenges him to a duel to the death. Perhaps some exposition, where we see that he really means it and won't back down for anything.
Back to present. We hear the challenge to a duel and the line "I could never love someone with blood on his hands" again, in voice over. The official starts the duel. Henry leaps in with a wild swing. Duelist ducks under swing, reaching down to crush a rose, and pushes Henry back as he stands up. Duelist throws rose petals in Henry's face, then runs from the duel. Henry then says that he'll let the Duelist run, but will kill him if he comes back, almost friendly now. Some more philosophy, maybe.
Possible lines:
(Beginning)
Duelist: Every now and then, we are given a choice--whether to hurt those who have hurt us, or to let them continue. To repay them for the flowers stolen, or to let them twist their knives in our wounds. It is human nature to choose the first--inevitably, all men do. I know--I have made a profession of hurting back, of killing. I am a duelist, settling disputes of "honor" for a tidy sum. This, however, this is my choice.
---
(Talking to Rose)
Duelist: So I've heard you fancy this Henry fellow.
Rose: None of your business, sir.
Duelist: Apologies.
Rose (somewhat playful): So you do know how to apologize. One wonders why you don't do that, rather than killing people who argue too much.
Duelist: Perhaps there's no money in it.
Rose: Perhaps if you'd studied law...
Duelist: Perhaps if I was Henry, you mean.
Rose: No! But now that you mention it, I might fancy him. Just a bit.
(Duelist looks upset)
Rose: What's wrong with that?
Duelist: Oh, just worried. He can't defend himself, you see.
Rose: Of course not! I could never abide a man with blood on his hands.
Duelist (even more upset, but hides it quickly): Hmm. Well, all the same, he should defend himself.
Rose: You're too worried. Besides, he has an unbridled passion about him--anyone who might try to fight him would surely be daunted.
Duelist: A hot head is soon lost.
Rose: Oh, no more of your silly proverbs.
---
(Henry discovering Duelist, Rose, after forcing them apart)
Henry: What the hell, man?! *slaps the Duelist* I thought you were a gentleman! I thought you trustworthy!
Duelist: I--
Henry: By God, what are you thinking? Infringing on her honor? Coward! I demand satisfaction!
Rose: Henry...
Duelist: A duel?
Henry: Yes, sir! To the death!
Duelist: I beg you to reconsider.
Henry: There is nothing--!
Rose: No, Henry, please don't...
Henry: There is nothing to reconsider!
Duelist: Very well, then, knives at dawn. I'll alert the official, he'll set the grounds.
---
If a rose garden is too much to find, then have the Duelist come on scene with a rose, which he can let drop to the ground before the fight begins. Otherwise, a simple pastoral scene could work--a farm, or a park.