I have a 30,000 mile honda fit 2015 lx, everyday driver, bought it at 12 miles. This especially happens when using then A/C.

I havent been able to find a thread on here that addresses this issue...

 

There is a recall on the 2015 coilpacks. Don't know if yours is affected, but living in Santa Ana and having the A/C on would stress the coilpacks if they're faulty. You might want to contact your dealer and have them take a look.

2015 Honda Fit recalled over ignition coils

 

If it's just the engine speed changing a bit when the AC compressor cycles on or off, that's perfectly normal and expected and nothing to be worried about.

 

 

Yup definitely more noticeable on smaller engine cars

 

The AC compressor requires quite a bit of engine power to run, you can definitely feel when it cycles on and off.

 

Gotta agree. Look into those coilpacks first. Had mine done 2 months ago and the engine is noticeably smoother (specifically from a standing start).
BTW, the Canadian dealer who worked on it was initially hesitant to perform the recall as I got a US VIN#. One phone call to Honda Canada and all was resolved.