What is your MPG? I'm thinking mine is low

congrats!
what brand and model tyre, and pressure you're running?

check the oil level and air and cabin filters.

 

This may not help as I live in West-Central Florida, which is fairly flat. I too bought a 2015 Prius Five in February and driving very conservatively I am consistently getting 55 mpg, which is about 4 mpg less than what the dash gauge says. I do the calculations by hand every time. I also had a 2010 Prius I bought used a year before this one and like it so much I upgraded to the 2015 Five. Loving it. I should also add that I use non-ethanol gas since I have owned it and that could be a reason for some of the improved mpg. The car is totally stock.

 

check the 12v health, sitting is bad for it.

 

get a digital volt meter, pop the hood in the evening, and open it the next morning to check the voltage at the jump point in the fuse box under the hood. don't bring the fob near the car, or open any doors.

 

Describe your driving habits, environment and surroundings, that will determine if something needs to be looked at. When I race through highway traffic at 75mph, net 45mpgs for an hour drive so thats pretty bad obviously but going 60mph, I can get 58 mpgs. City traffic itself, maybe 62mpg-ish. Modes to me dont matter long as you get up to speed and EV it.

Last OCI, I'm 1550 mi @ 60.1 mpg. Redline 0w-20

 

5 minutes of operation per weekend won't keep the 12V battery adequately charged. The internal charging is quite slow. If it isn't used much, an external battery charger or tender will do much better.

Check also for brake drag. The brakes and wheels should not be getting excessively hot during normal driving. Use your older Prius as a reference for comparison.

In 'normal' driving, apart from expert hypermiling, the Gen3 should be getting 5-ish better MPG than the Gen2 when driven the same way in the same conditions. But under expert hypermiling, that difference could shrink or nearly vanish. Only in the most extreme cases should the Gen2 beat the Gen3.

This questionnaire is meant for new first-time Prius drivers, not longer time owners who have changed Prius models. But it may still give you some ideas for what else to check:
Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat

 

I live in Central Fl.,have 106,000 miles on my 2010 Prius,and get 52 mpg in mixed driving,50 mpg on the highway,and 57 mpg in city
driving. Since I just bought tires with a 500 treadwear rating my mpg has dropped about 7-8%. The computer is off by about 3-4 mpg
since I bought the car in Sept.2009. Great car,a little tough on tires,but very economical in hot weather.

 

My mileage started to get pretty bad when my 12v was about to meet its end. I ran it until it died completely (not recommended...had to take an Uber to and from work, and an Uber to go get the battery).

Under normal driving and temperature conditions (Ohio) I usually get 49-50. I don't do anything special except normal techniques used by Prius owners. I don't over inflate my tires any more. I have a Scan Gauge, but no longer use it.

Side note... I was able to raise my MPG by 2.5gal at the 120-160 miles per tank mark. First time I tried that. Drove 55 both ways for 40-50 miles.

 

We're gonna hold you to that...

You might also try a does of fuel injector cleaner (look for one with PolyEtherAmine), the kind you add to the tank at fill-up. Just follow the directions, if you need to measure it out, stick to the recommended amount. I found our spring pick-up in mpg kinda absent this year, so gave this a try, seems to help.

Also: there's a couple of bugbears with the 3rd gen: the intake manifold tends to get really oil-socked by Positive Crankcase Ventilation system, and the (new for 3rd gen) Exhaust Gas Recirculation system is problematic, prone to inexorable clogging up. A couple of links regarding those:

EGR & Intake Manifold Clean Results | PriusChat

Oil Catch Can, Eliminate that knock! | PriusChat

 

i get 50 to 53 mpg depending on the the number of hills in my stock 2010 with 225k miles... keep in mind Toyota's programming is severely limited(idiotic) ,the cruse control is very aggressive and the accelerator peddle way way too sensitive i am often only using it at 1% to 10%.

 

Ive owned a camry and driven numerious family member other toyotas and rental, the cruise resume is actually efficient. When I try to accelerate back to cruising hwy speed, the resume gets better mpgs than numerous manual resume pedal acceleration.

 

2015 Prius Two. Averaging 56.3 MPG for the last reset of the trip odometer. There are some trips where I am getting 72MPG.
I pay attention to my driving and travel the back roads where the speed is lower and I can run in electric mode.
The Michelin Energy Saver (not AS) tires really helped with about a 4 MPG difference from the Goodyears that were from the factory.

 

I've got a 2015 Prius Three with almost 60k miles and have driven it pretty conservatively since I bought it a year ago. I've just bought a new set of tires - Yokohama Touring-S in the stock size, which I believe is what it originally came with. I've averaged 56 mpg; the only change I've made is to raise tire air pressure to 49 and 47 psi, front and back, since I noticed that the sidewall says maximum psi can be 51 (!!). Don't know if I'll keep 'em that high or not, but we'll see......