Here's something to clear up the total pot size:

Pot at $4 before flop.
Villain bet 4, I made it 8
He then matched the 8 (4 more), and THEN put 15 more to go.

So, the total pot was 4+4+8+4+15 = $35 total.

To me, it would have cost 15 to call his all-in, so 15:35, which is just a little worse than 1:2.

I'm not quite sure how this is an easy call.
There's a good chance he has some kind of made hand, which means I'm relying on draws to survive. He's also already all-in, so I have no chance at him folding, and no chance at making any more money.

Does it make more sense to pick my battles in better situations? This doesn't seem like a large +EV situation to me.

It's probably slightly positive....but why risk the majority of my chips on one big hand?