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 2 oppenents a raise becomes +EV because you are getting 2:1 on all bets on the turn (if 2 other oppenents) when you are only a 1:1 shot. Is this correct?