EV of open-ended + flush draw

[ZManODS]

Say you are on the turn with 3 other oppenents and are last to act. Also lets say you have the good fortune of having an open-ended draw plus a flush draw (15 outs .85:1). If the first person bets and the other 2 oppenents call should you raise for value here?

How bout with only 2 other oppenents. Basically what i am asking is whether this move is +EV and if not, how many people do you need to have to make it +EV.

My thinking: I think with 3 or more oppenents a raise becomes +EV because you are getting 3:1 on all bets on the turn (if 3 other oppenents call) when you are only a ~2:1 dog. Is this correct?

[IsaacW]

Are you on the turn or the flop here? 15 outs is 0.85:1 with two cards to come (the flop), but only 2.06:1 with one card left (the turn).

[Lost Wages]

See this chart. On the turn, if you have more opponents than your turn to river odds then you can raise for value. On the flop, use the flop to river odds. In both cases it is assumed that you will always win if you make your hand which of course isn't true unless you are drawing to the nuts on the turn so you should round up a little.

Lost Wages