[[MM]RoXoR[FS]]

I think you should create an array of position's you want like

pawn Code:

new Float:pos[15][3] = {
{0,0,0},   //Replace 0,0,0 and 1,1,1 with position's 
{1,1,1},   //Do for all 15 positions
.
.
.
};

Now create a timer when game start's

pawn Code:

forward StartFire();

public OnGameModeInit()
{
    SetTimer("StartFire", 15*60000, 0)
}

Now the function to create object

pawn Code:

public StartFire()
{

    for(new i=0;i<3;++i){
    new rand = random(sizeof(pos));
    CreateObject(18689,pos[rand][0],pos[rand][1],pos[rand][2],0,0,0);}
}