A forward cg will make the airplane pitch more with changes in power setting, but should not make it more sensitive to elevator input. I would first balance the airplane as close as possible to the position shown on the plans. Then be sure that the control throw with the transmitter on high rate is equal to or a little less than called for on the plan.
If it’s not, reduce elevator travel by moving the pushrod to the outermost hole on the horn at the elevator, and/or moving the pushrod to a hole closer to the center at the servo. Then when you put the transmitter on low rate the elevator should be a lot tamer. There is nothing inherent about a low wing that makes it more sensitive to elevator input. Although I haven’t flown the Cherokee, it is a sport model with a conventional setup and should be about as easy to fly as your trainer. The main difference would be lateral control. The wing is flat (no dihedral, I'm assuming you have the Hangar 9 Cherokee) and you will have to constantly control bank with the ailerons. This will keep you busy at first, but you’ll quickly adjust.