Higher gears are definitely required with the ax15. I was running 3.23’s in my Duster and still only using 1st gear if I was taking off on a hill. I’ve since installed 2.76’s and now use 1st through 5th gears as intended.
I had 3.07s in a wrangler with the AX15 and 5th was all but useless under 55 with a stick 4.0 inline 6 and 235 15 tires even more so with the 31/10.50s I had on it for a while.
I wouldn't worry about an OD trans with gears (numerically) lower than 3.21/3.23.