Since the creatures are so small, they could have very easily been thrown in through various scenes on different planets as a sort of easter egg / sight gag, but what you see in the trailers is basically what you get.
If you’re still having flashbacks to Jar Jar Binks appearing in The Phantom Menace trailers, you can safely put those to the back of your mind.
In fact, the only plottery that the little beasties seem to be involved in, besides some smaller bits inserted in other scenes, is a running gag with Chewbacca.
As we see the co-pilot of the Millennium Falcon ready to chow down on roasted Porg, a pack of them watch on in horror as he’s about to tear into his meal.