We have a 2010 RX 350, and I am very disappointed in our MPG. We do live in Wash DC, and our daily commute take us up and down a number of inclines (small hills)within the city. But I never expected MPG of 15.6 - 16.9
15-17 mpg is pretty typical for stop and go driving with a 3.5l V6 mid size crossover these days. That’s the price for all that hp and weight, especially in cold weather. Is it awd? That costs another mpg or so.
I just looked it up, and it’s only rated at 18 mpg around town. City driving in hilly terrain can be expected to make it worse. It may improve a bit once it’s broken in, but don’t expect much. This is by no means designed as an economic vehicle.
Sorry.
Congratulations, you bought a luxury vehicle with a 3.5 liter V6 and 275 horsepower. I think about 16 MPG is what I would expect. You can’t get a 4,200 pound vehicle from 0 to 60 MPH in 7.5 seconds without compromising fuel economy, but at least it holds 20 gallons of fuel.
As The Same mountainbike said the vehicle is rated for 18 MPG city. 15.6-16.9 MPG is in the ballpark when you take winter fuel and some hills into account. What kind of mileage were you envisioning getting when you bought this vehicle?
What did you expect? Unless you got the hybrid I wouldn’t expect anything under 20 mpg with your type of driving.
I’ll trade you even up for my 4 cylinder RAV. It gets much better mileage for your short trips. Meet you in Chicago and bring your title. 
but would you want the payments and/or increase in insurance 
The EPA rates your SUV at 18 MPG in the city. But their simulated driving test is not necessarily identical to the way you drive your car. I looked up older actual mileages for the RX350, and some people had mileage as low as yours.
“but would you want the payments”… I’ll have the title,why would I want to make any payments ?
Even without getting into any “hypermiling” techniques, the driver is as important to fuel economy as the car. I can get 8 mpg better than EPA fuel economy in my Accord, and 3-4 mpg difference is easy in any car. And it’s just as easy to get worse fuel economy. Unless you’re sure you are driving an economical fashion, don’t blame the car.
Get a Scangauge. http://www.scangauge.com/ It will tell you your MPG at any point in your driving, and you can use that information to figure out what you’re doing wrong.
Don’t accelerate too fast, don’t accelerate too slow. When you’re coming out of a stop light, about 1/4 to 1/3 of red line is where your RPMs should be. Don’t brake unless you have to, and then do it early and smoothly. A light touch on the brake and the gas is the best way to good fuel economy.
If you DO optimize your driving habits, THEN start trying to figure out what is wrong with the car. Oh, and a Scangauge can help you do that, too. (Or, you know, the dealer could, since the car is under warranty.)
I would like to add that bringing in a car for warranty work when nothing is wrong can cost you. Repairs (parts and labor) are covered under warranty. However, if they find nothing wrong, you should expect to pay for the diagnostic work.
As cool as that ScanGauge is, I cringe when I imagine a driver staring at the fuel economy read-out instead of paying attention to traffic, so please be careful not to spend too much time looking at it while you drive.
I agree, driving technique makes a HUGE difference. I have a similar crossover, and I can get 15 mpg or 19 mpg around town, depending on how I drive it. I imagine the RX350 has an mpg readout of some sort, the OP should use it to help adjust their driving style.
To be realistic, I have a similar size weight, power Toyota vehicle and would be happy to get 16.9 mpg around town in the winter. That’s why I joke about going to 4 cyl. You got it, and unless you want to trade, deal with it, but don’t expect much “hypermiling” improvement. You bought this vehicle for reasons other than mileage, enjoy them.