JK wheels will work on a JL. At least the ones we had did.
JL Wheels have a slightly larger stud bore than the JK but they will fit. It may require running a drill bit through them lightly just to deburr the old holes. There will likely be burrs on the wheel if they were previously mounted because of where the lug nut taper presses against the wheel and mushrooms the wheel material. We had wheels on our JK that we put on our gladiator and I had to deburr the holes. It didn't remove any wheel material in an unsafe manner; basically just cleaned up the holes. But the wheel studs on the JT are longer so you cannot use JK lug nuts. Plus the JL is a 14 mm stud where as the JK studs are smaller than that so you'll need JL lug nuts anyways.
Then, because we liked the wheels so much, when we bought our JL, we bought another exact set of wheels and put them on our JL and I didn't have to debur them at all. Wheels slid over the studs just fine.
Both of these Jeeps are running the exact same JK wheel:
We had stock JK wheels on our JLUR. The wheels fit fine on the Jeep, EXCEPT for the spare tire carrier! The center hole for the JK wheel is smaller than the JL hole. If you're running the stock spare tire carrier on your JL you're going to have to sand down the tire carrier post or really bore out the center hole.
I choose to concentrate on the post so I didn't make the wheel hole too loose and lose the center caps.
It's not just a Jeep, it's an amusement park on wheels.