could someone jus help me out.for a 15' wheel is there a correct offset to use????

 

this might not be the best place to ask, try the wheel & tire

 

The ideal offset is the same as your existing or standard wheels. These have been designed to provide good handling and safe steering geometry for your car. Having a large offset (or inset) can give unpredictable and possibly dangerous handling.
So, you should ideally keep the offset near to standard, but with wider wheels, just make sure there's clearance for the shock absorber and wheel arch, plus the lower arm and inner wing on full-lock