[Balimbanana]

Try changing the "duration" key to "health" instead,
then add "spawnflags", "4" for Start On or you might have to do an
ActivateEntity(g_iEntityIndex); and an AcceptEntityInput(g_iEntityIndex,"StartFire") ; after DispatchSpawn.
In code block:

	g_iEntityIndex = CreateEntityByName("env_fire");
	DispatchKeyValue(g_iEntityIndex, "firesize", "72");
	DispatchKeyValue(g_iEntityIndex, "health", "15");
	DispatchKeyValue(g_iEntityIndex, "damagescale", "0.0"); //Might not work as intended
	DispatchKeyValue(g_iEntityIndex, "LightRadiusScale", "1.5");
	DispatchKeyValue(g_iEntityIndex, "spawnflags", "4");
	DispatchSpawn(g_iEntityIndex);
	ActivateEntity(g_iEntityIndex);
	AcceptEntityInput(g_iEntityIndex,"StartFire"); //Might not be needed with spawnflags 4

Edit: Oh, and you might also want spawnflags 128 to remove itself when it goes out, so it doesn't use up more edicts every time it is spawned and goes out. So you would change the spawnflags to 132 instead for that.