You guys ended up with some pretty high Passive Perception scores, so I was struggling with how to use those. Do you, in effect, just always see the DC15 trap if you have a PP of 16? So, after some reading, I think what I'll do is let PP give you general information. For specific information, you'll have to roll. So, you don't automatically know where the hidden goblins are just from your passive perception. You just know that someone's over there. If you want to roll to see if you can pinpoint them, you can, but you'll have to roll for it.
In effect, this may turn out to be the exact same thing as telling you outright, but at least it gives you a slight chance of failure and makes things more interesting.