Proper Tire Size and its effect

It is their mistake right size is 195/65R15. I'd go back and insist on replacing tires with proper size.
We are talking about 2% error, but the biggest issue if you have to replace one tire at some point and someone puts a right one. Also donut spare is usually sized to match OEM wheels.

Here is size comparison calculator:
Tire Size Comparison

 

The correct size tyre is also a little stronger than the size smaller. Get the correct ones installed.

So a tyre shop, whose business is knowing what size and type of tyre to put on each vehicle messed up? Hmmm.....

 

You'd think, right?

Not to worry they can do even worse. Had managed to break off TPMS sensor while mounting/dismounting tire. By the time it stopped working 12mo later it was too late to take it back.

 

Yeah, this is a slamdunk: go back, get it done right. They really screwed up: the correct size is in the door jamb, for starters.

Trading horror stories: Costco sent me on my way with 3 rights and one left, in the (directional) Michelin X-Ice, one time.

 

The 185 tire has a smaller circumference than the 195 (you can find a tire size calculator on tirerack dot com), thus your speedo will indicate you are going faster than the car actually is traveling. One revolution of the smaller 185 tire will not take you as far as one revolution of the 195. Also, this is why your spare tire (donut) will not match the circumference of the new 185 tires.

More important is the load rating. Check the load rating on the new tires. It's stamped on the sidewall along with the max tire press allowed. Then make sure it is at least half the larger of the two axle ratings stamped on the front door pillar. For example, the OEM tire is rated at 1279 lb, and the beefier of the two axles (the front) is rated at 2270 lb, so the OEM tire (combining both front tires) can support the max load rating of the front axle. And keep in mind, if you're running the max axle load, your tires should carry the max allowed pressure stamped on the sidewall (44 psi) for the OEMs.

If it were me, I'd have them replace with the correct size tire...

 

Definitely go back for the correct size (or better). Besides considerations others have already mentioned, the undersize tires will not last as long, and will run hotter (other things being equal).

 

I have a tire changer, so these days I buy online and mount my own tires. When I've gone to tire shops, I've always told them what tire size I want, "do you have this tire brand/model in this size? How much "out the door" for 4 tires? "

I agree with others, go back and get the correct size tire. I would be irritated for the next 3 to 5 years driving with the wrong tire.

Sorry you need to waist a few hours for their mistake.

 

The 195/65R15 has a 635mm diameter. The 185/65R15 has 621mm diameter. The cars computer will calculate the mileage and odometer with wrong data. Change it to the right size.

 

Take them back. There is no room for doubt about the right size. Any confusion was in their minds alone when they made the mistake. If they don't have the right size in the tire you chose (may be the reason it happened), get them to put on Michelins. I believe that Defender, Premier or Primacy are all good and many here like the Energy. I would check proper price differentials before going so I would be ready to bargain.

 

I chose 185 tires in an effort to lower rolling resistance. After all, wider tires cause a drop in fuel economy.

 

Under certain assumptions, yes. In this example, no.