Can I put 235.75 x15 tires on my 2003 tracker? Would this cause a problem

That year tracker came with anywhere from a 195 to a 215 depending on the model. If you put a 235 on there, you'll not only gain width but overall diameter and height. If this tire fits in the wheel well without rubbing (especially on turns and bouncing) you will effect your speedometer. You will show you are going slower than you really are. No one can tell you if this is going to work without modifications because your suspension my have some sag to it and although it may fit standing still, once you drive, turn and bounce, things may change. You will have to try them on, and before you drive it, turn the wheel lock to lock checking it as well as bounce it during the lock to lock turns.