After 15 games you're only just starting to feel the tactics, so the base game's got plenty of life left in it!
But here's the thing: once you get tired of it, expansions don't always save the day - sometimes they just complicate things for no reason, and sometimes they actually become the whole point, like you need an entire system like Kings and Castles or Traders and Builders to make it work! Try sticking with the base game for a couple more months, then you'll have a better sense of which expansion is actually worth grabbing.