Firstly gearing is a personal thing so there are no hard and fast rules.
I would go lower if you've never ridden SS or fixed. Mashing a big gear is a good way to injury yourself as well as make it difficult to gain handling skills to ride the bike.
48x15 is close to track gearing which is great if you don't have to stop and start all the time. But unless you're very fit or young, riding that higher a gear in urban settings will hurt, maybe not now but in a few years time. Again, this is personal opinion.
Its best to start lower, build up your strength and speed, work on your spin and then move higher. But as I said gearing is a personal thing.
fixedpip is right, don't injur yourself
I'm sorry if I sounded suggestive in that way. Even I myself had a little training before riding the 48 / 15. I was commuting on a MTB in top gear and never switching out. I can't say that my legs didn't hurt for several days either because they did! Do what your body tells you and don't jump in too fast.