Basically, you name a requirement for a card, the next guy makes a card that fulfills those requirements. Try not to make the requirements too specific though, a good guideline would be to ask for something with no more than 4 of the following:
1. Card Type (Weapon, Minion or Spell), 2. Class, 3. Tribe, 4. Statline/Mana cost, 5. Specific synergies (i.e. a card that works with Onyxia, etc.)/General synergies (i.e. supports Pirates, etc.), 6. Or has Battlecry/Deathrattle/Inspire/whatever other Keyword.
Like, say someone wanted a 0 Mana 12/12, then I'd make
I feel like that's a little OP -- it has the potential to be an 11/2 for 3 mana if there's another minion. Maybe -3/+1? So if there's three other minions then it's a 3/3 with Taunt, if there's two other minions it's a 6/2 with taunt, etc.
Anyway! Considering you asked for 15 Health, I figured I'd do a replace-your-hero-with minion. Here he is.