yes, so let's say we up the stakes... calling $3 with 44. (I'm not sure what stakes you're playing with only $15, maybe .25/.50 with min buy in.) So you have 13.33% chance of hitting a set on the flop, meaning you must call 7.5 times in order to hit a set.

$7.5 x 3 = $22.5, and when you hit, you can put them all in for more than that?

I hate playing them because it shows weakness when you just fold right after missing the flop. There are almost always overcards, and you can't really bet aggressively, knowing you have the best hand. If they call, what are you going to do? Bluffing or semi-bluffing is expensive, and I do not recommend it. Also, there is no guarentee that they will move all in.