15.5 rounded to the nearest tenth

The tenths place is to the right of the decimal point.
In order to round u number to the nearest tenth, you should to the right of the tenths place. Depending on this number you should determine if you will round up or stay the same (if it is bigger than 5 you will round up, if not it will stay the same).
In our case, the number is 15.5 so it is already rounded to the nearest tenth.