what size are the tires? what brand are the tires? how much do the 15s weigh? how much do the 16s weigh? there are too many factors with such little info. for instance the weights may be the same but you may have shitty tires on the 15s and great tires on the 16s. or you may have lightweight 15s and heavy chrome 16s. the size of the tires will make a difference depending on the sidewall height and how much air pressure is in them.