Betting vs calling with a draw

[HouseCalls]

OK first of all this hand never happened. I'm making this up as a hypothetical situation to help me clarify something that Mr. Wookie was trying to explain to me the other day. So here goes:

Hero UTG+1 with J [img]/images/graemlins/heart.gif[/img] T [img]/images/graemlins/heart.gif[/img]
UTG fold, Hero calls, EP2 calls, MP1 raises, MP2 calls, MP3 calls, CO calls, Button calls, SB calls, BB calls, Hero calls.

Flop (18SB; 9 players) 8 [img]/images/graemlins/heart.gif[/img], K [img]/images/graemlins/club.gif[/img], 9 [img]/images/graemlins/heart.gif[/img]
Hero checks, EP3 checks, MP1 bets, MP2 folds, MP3 calls, CO folds, Button raises, SB folds, BB folds, Hero calls, EP3 folds, MP1 calls, MP3 folds.

Turn (12BB; 3 players) 3 [img]/images/graemlins/spade.gif[/img]

Ok here is the question: What to do here. My usual method of evaluating this has been to say that I have 15 outs (9 [img]/images/graemlins/heart.gif[/img]s, plus 3 non [img]/images/graemlins/heart.gif[/img] Q's, and 3 non [img]/images/graemlins/heart.gif[/img] 7's) At 15 outs I'm about 2.1:1 to make my hand. With 12BB in the pot I bet.
Now Mr. Wookie suggested that whether or not to bet is not based on pot odds but depends more on how many callers you expect. Thus in this example with 15 outs I'm about 30% to make my hand so I need to have at least three callers since there are only two players left I can't bet here.

Is this logic correct for deciding whether or not to bet???

Ok say I don't bet and the action is as follows:

Turn (12BB; 3 players) 3 [img]/images/graemlins/spade.gif[/img]
MP1 bets, Button raises, Hero?

Now there are 15BB in the pot and I have to put in two bets. I'm still getting 7.5:1 and the break even odds for my hand are 2.1:1 so I can call.

Is this right?

I'm still very new and fairly confused to the idea of using pot equity for betting decisions and pot odds for calling decisions.

Does this make sense or am I still confused??