100NL 6max AA too passive?

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My first serious 6max session. Reads are: all seem to be non-dangerous donkeys...

too passive? where to get more agg? When he checked behind on the turn I was pretty sure I had him beat but did I bet too little?

No-Limit Hold'em, $1.00 BB (5 handed) FTR converter on zerodivide.cx

saw flop|<font color="#C00000">saw showdown</font>

<font color="#C00000">UTG ($111.00)</font>
<font color="#C00000">MP ($24.00)</font>
Button ($77.00)
<font color="#C00000">Hero ($158.00)</font>
BB ($100)

Preflop: Hero is SB with A[img]/images/graemlins/club.gif[/img], A[img]/images/graemlins/heart.gif[/img].
<font color="#CC3333">UTG raises to $2</font>, MP calls $2, <font color="#666666">1 fold</font>, <font color="#CC3333">Hero raises to $6</font>, BB calls $5, UTG calls $4, MP calls $4.

Flop: ($24) 8[img]/images/graemlins/heart.gif[/img], Q[img]/images/graemlins/diamond.gif[/img], 7[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
<font color="#CC3333">Hero bets $18</font>, BB folds, UTG calls $18, <font color="#CC3333">MP raises to $18.16</font>, Hero calls $0.16, UTG calls $0.16.

Turn: ($78.00) 7[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
Hero checks, UTG checks.

River: ($78.00) 6[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">Hero bets $15</font>, UTG calls $15.

Final Pot: $108.00