Hi and welcome . You can’t change to 15” wheels because of the front brakes callipers size, smallest possible size that you can fit is 205/55 R16 , but in my opinion don’t change anything, just get quality tyres that are rated for low rolling resistance and quiet , Good Year Efficient Grip Performance are good example or Kumho Ecsta HS51 if you are on a budget, and most importantly is to keep them to the right pressures, not much above or below max allowed .