TPTK facing a min raise on flop

[LuckyDevil]

Villain (CO) is unknown.

I just sat down less then ten hands ago. I have raised preflop my last two hands, so this is my third hand in a row that i am the PFRr. Neither of my other two hands went to SD. The first one i check/folded and the second one i took down on the flop heads up. The BB (fish) has cold called all of my previous PFRs. I have not yet played a hand with CO.

Full Tilt Poker
No Limit Holdem Ring game
Blinds: $1/$2
6 players
Converter

Stack sizes:
Hero: $231.65
UTG+1: $129.20
CO: $187.40
Button: $155.30
SB: $198
BB: $67.30

Pre-flop: (6 players) Hero is UTG with A[img]/images/graemlins/diamond.gif[/img] K[img]/images/graemlins/heart.gif[/img]
<font color="#cc0000">Hero raises to $7</font>, UTG+1 folds, CO calls, 2 folds, BB calls.

Flop: 4[img]/images/graemlins/club.gif[/img] K[img]/images/graemlins/club.gif[/img] 8[img]/images/graemlins/diamond.gif[/img] ($22, 3 players)
BB checks, <font color="#cc0000">Hero bets $15</font>, <font color="#cc0000">CO raises to $30</font>, BB folds, Hero????