I find 47x15 a good velodrome and tailwind commuting gear, but I like 47x18 for most rides (I’ve hit 59.8 km/h on it). Go a 16 t, it will feel like a big difference without being too shit into headwinds and uphill.
Just be aware that you will have only 3 skid spots on 48x16.
I’d stay with what you’ve got. I recently went from 48x16 to 48x19 and probably wouldn’t go back lightly. I feel the wind limiting my speed more than spinning on the flats. And on downhills I don’t have a need to go faster than 40-50 on a fixed gear with only a front brake.