15/15/15 100% Gloom Lvl 7 - Evolve?

if you have 2 Plante type attack, go powerup, for kill vaporeon.
if you have 1 poison attack (safe your stardust), stay your villplume on your collection.
if you have moonblast (i got 6 times moonblast -_- 93-96%)
you can hang yourself ;-)

I would definitely not waste my candies nor stardust on this pokemon. As you state, Oddish are quite common. you should be able to find another 82+ IV oddish/gloom which is significantly stronger.

Definitely worth keeping in the event that trading gets implemented.

As for powering up, probably not. Like you said you're low on stardust. If you already have tons of powerful pokemon that are maxed out then you could save up to power up the Vileplume if it gets a good moveset, but Vileplume isn't anything special. There are other grass pokemon that basically do the same thing - Victreebel / Venusaur. That limited stardust you have could be better spent on an already high level pokemon.

I'm sure you'll find an Oddish in the wild with good enough IVs that will be already high level, which will save you a lot of candies and stardust. Oddish have the second highest base capture rate for some reason, behind Magikarp, so even high level Oddish are easy to capture with just Razz + Great Ball.

https://pokemongo.gamepress.gg/base-capture-rate

I would evolve it to just get another prestiger...no need to power up since there are more powerful grass types, but since you say oddish candy is easy, might as well for exp and all...could also leave in gloom for if you like to have a live/active dex (I do this).

https://pokemongo.gamepress.gg/cpcalc#/
With the CP calculator here, you can see that it will evolve to 486 CP with 57 HP. So if you get a good double grass moveset, you will still need to invest some stardust to even allow you to prestige with it against most Vaporeons.

Also, if you are evolving just for training, Razor leaf is a little awkward when attacking because of the long animation time. An Ivysaur, Venusaur, or Tangela with Vine whip+Solar beam is a little easier for attacking and Vine whip charges energy faster.

Another point, you might also consider keeping it as a Gloom for now to try evolving into Bellossom when gen2 comes out.

Why not evolve it? There is no reason to hold back really, especially since Odish are common in your area. If you get a terrible move set, just keep it in hope for move rerolls in future. If you get good attacks, you can either power it up when you get Stardust or keep it for future use. Perfect IV pokemon are a collectible, and will definitely be sought after if/when trading comes.