Nonsense to the 10,000 mile theory. As far as the OP's mileage, what did expect from stop and go city traffic? I say 15 is pretty good.
First month I had my car, I got high 20's on an all highway road trip. It did improve marginally after that, but it certainly didn't take 10,000 miles to reach into the high 20s. By 2,000 miles it was good to go. It really hasn't gotten any better since then.
Actually, a little worse, but the tires affected it, so no problemo.
From Fuelly, my first few fill ups:
<table border="0" cellpadding="0" cellspacing="0" width="930"><colgroup><col width="49"><col width="72"><col width="44"><col width="54"><col width="64"><col span="2" width="111"><col width="64"><col width="361"></colgroup><tbody><tr height="20"> <td style="height:15.0pt;width:37pt" height="20" width="49"> mpg</td> <td style="width:54pt" width="72"> odometer</td> <td style="width:33pt" width="44"> miles</td> <td style="width:41pt" width="54"> gallons</td> <td style="width:48pt" width="64"> price</td> <td style="width:83pt" width="111"> fuelup_date</td> <td style="width:83pt" width="111"> date_added</td> <td style="width:48pt" width="64"> tags</td> <td style="width:271pt" width="361"> notes</td> </tr></tbody></table>
<table border="0" cellpadding="0" cellspacing="0" width="930"><colgroup><col style="mso-width-source:userset;mso-width-alt:1792;width:37pt" width="49"> <col style="mso-width-source:userset;mso-width-alt:2633;width:54pt" width="72"> <col style="mso-width-source:userset;mso-width-alt:1609;width:33pt" width="44"> <col style="mso-width-source:userset;mso-width-alt:1974;width:41pt" width="54"> <col style="width:48pt" width="64"> <col style="mso-width-source:userset;mso-width-alt:4059; width:83pt" span="2" width="111"> <col style="width:48pt" width="64"> <col style="mso-width-source:userset;mso-width-alt:13202;width:271pt" width="361"> </colgroup><tbody><tr style="height:15.0pt" height="20"> <td style="height:15.0pt;width:37pt" align="right" height="20" width="49">0</td> <td style="width:54pt" align="right" width="72">311</td> <td style="width:33pt" align="right" width="44">0</td> <td style="width:41pt" align="right" width="54">13.928</td> <td style="width:48pt" align="right" width="64">3.599</td> <td class="xl63" style="width:83pt" align="right" width="111">7/13/2011</td> <td class="xl64" style="width:83pt" align="right" width="111">7/13/2011 17:45</td> <td style="width:48pt" width="64">
</td> <td style="width:271pt" width="361">
</td> </tr> <tr style="height:15.0pt" height="20"> <td style="height:15.0pt" align="right" height="20">24.873</td> <td align="right">487</td> <td align="right">176</td> <td align="right">7.076</td> <td align="right">3.589</td> <td class="xl63" align="right">7/16/2011</td> <td class="xl64" align="right">7/16/2011 7:16</td> <td>
</td> <td>Bj's osceola pkwy</td> </tr> <tr style="height:15.0pt" height="20"> <td style="height:15.0pt" align="right" height="20">26.613</td> <td align="right">935</td> <td align="right">448</td> <td align="right">16.834</td> <td align="right">3.699</td> <td class="xl63" align="right">7/17/2011</td> <td class="xl64" align="right">7/17/2011 7:47</td> <td>
</td> <td> Drive to Pensacola.</td> </tr> <tr style="height:15.0pt" height="20"> <td style="height:15.0pt" align="right" height="20">27.683</td> <td align="right">1407</td> <td align="right">472</td> <td align="right">17.05</td> <td align="right">3.599</td> <td class="xl63" align="right">7/18/2011</td> <td class="xl64" align="right">7/18/2011 5:41</td> <td>
</td> <td>Drive back from Whiting Field. Hit by falling tree on I 10.</td> </tr> <tr style="height:15.0pt" height="20"> <td style="height:15.0pt" align="right" height="20">21.378</td> <td align="right">1595</td> <td align="right">188</td> <td align="right">8.794</td> <td align="right">3.639</td> <td class="xl64" align="right">7/28/2011 9:00</td> <td class="xl64" align="right">7/29/2011 7:15</td> <td>
</td> <td>Driving around town</td> </tr> <tr style="height:15.0pt" height="20"> <td style="height:15.0pt" align="right" height="20">30.08</td> <td align="right">2070</td> <td align="right">475</td> <td align="right">15.791</td> <td align="right">3.689</td> <td class="xl64" align="right">7/29/2011 22:00</td> <td class="xl64" align="right">7/29/2011 17:57</td> <td>
</td> <td>drive to pensacola</td> </tr> <tr style="height:15.0pt" height="20"> <td style="height:15.0pt" align="right" height="20">29.184</td> <td align="right">2561</td> <td align="right">491</td> <td align="right">16.824</td> <td align="right">3.619</td> <td class="xl63" align="right">7/31/2011</td> <td class="xl64" align="right">7/31/2011 8:30</td> <td>
</td> <td>Drive back from Whiting Naval Air Station. All highway.</td> </tr> <tr style="height:15.0pt" height="20"> <td style="height:15.0pt" align="right" height="20">22.287</td> <td align="right">2938</td> <td align="right">377</td> <td align="right">16.916</td> <td align="right">3.539</td> <td class="xl63" align="right">8/6/2011</td> <td class="xl64" align="right">8/6/2011 13:11</td> <td>
</td> <td>
</td> </tr> </tbody></table>