If you are doing the chain at the same time, which is recommended if you have some miles on the bike, replace the front with another 15t, and go up several teeth in the rear.
You need a new chain usually to go up teeth in the rear, but it is worth it. Staying odd-# and odd-# rear ensures that the inny-vs-outy parts of the chain alternate on the same tooth of the gears, providing more even wearing.
Food for thought!