Have 2003 jetta vw inside to inside rim measures 16" but will the 15" covers fit

The two digits after the R is what size the tires AND wheels are - even if they have been changed from original equipment. Examples > 195/65 R15 > equals 15 inch tires AND wheels ... 205/55 R16 > equals 16 inch tires AND wheels.

Found this bit of information (with pictures) that should also help: https://axleaddict.com/cars/Tire-Sizes-What-the-numbers-mean