Yeah, that looks like a basic issue, simply old leaves falling off. It's because the leaves are entirely brown. But in future you should be cautious if the leaves are partially brown or have brown spots or the brownness isn't limited to lower leaves only. That's when you'll have to worry about your watering - maybe too much or too little. Otherwise, your location is great and the fig has a great sunlight exposure. And yeah, the repotting in spring is a great idea, it rejuvenates the soil and keeps the fig fresh. You're doing alright.