I have a low wing aircraft that had a poor roll-rate.
I re-engined it with an OS FS-91 IIP which was a bit lighter than the original Laser 91. The CG moved aft a little. The roll-response was much improved.
So, it may be that your CG position is well forward. This causes a higher angle of attack (because the tail is producing down-thrust) and modifies the airflow over the ailerons, making them less effective.