2015 Corolla - Bad Gas Mileage???

We bought a 2015 Corolla LE Plus this past Thanksgiving weekend. The tank went from full to ¾ full after 38 miles of city driving. The onboard MPG calculator said it was getting 16 MPG (it’s rated 29 city/38 highway. When we took it back to the dealer the sales consultant said that’s normal – that it would improve after it got “broken in”. The car mechanic who I have taken all my Toyotas to and who has only worked on Toyota for the last 30 years says plus or minus a couple MPGs would be reasonable but not minus 13 MPG. We drove it another 400 miles to “break it in” and during this breakin period it did get close to 38 MPG when we drove on the highway. Then I topped off the tank with gas, recorded the odometer mileage, zeroed out the onboard trip mileage recorder and the MPG calculator and my wife drove 61 city mileage. The onboard MPG calculator said it was getting 16.8 MPG and 61 miles divided by th3 3.854 that it took to top it off again = 15.8 MPG. Either way I don’t think the mileage should be this bad. Can anybody post new Corolla mileage you have experienced? - Thanks.
How cold was it during your city driving? How many occupants? How bad was the traffic and stop lights? From your highway mileage it sounds like your car is capable of delivering the proper gas mileage. I average over 45 in my ECO but I drive almost exclusively hi way and conservatively. Your mileage will take a big hit in stop and go city driving, but the seems excessive. If your driving habits are aggressive, weather is very cold, and your sitting idle in traffic for long stretches, have the defroster on, causing the AC to run, it might be possible to drop that low. Are you letting the car idle to warm up for several minutes? Any time you're not moving, your MPG is zero and can really kill your mileage. I don't thin your car has a problem based on your highway mileage. Consider your and your other drivers' driving habits, to be sure you're not wasting fuel.
Your highway mpg shows that there is nothing wrong.
In city, it might vary a lot but stop and go (especially if agressive - meaning breaking at the last minute instead of coasting and flooring instead of progressive acceleration) kills MPG

Corolla Cop

2014 Corolla S Plus
You are going to have to drive out several tanks before it will settle down. It will improve. Never trust the on board mpg display. It is usually several mpg's off. You need to calculate it manually if you want as close to accurate as possible mpg's.
While its sitting there warming up, it is getting exactly 0 mpg. Do that for 5 or 10 minutesand you're definitely gonna take a hit mpg wise.