It seems like you have two different questions here.

Was America isolated during history till its discovery in the 15th century?

More or less. There are cases of incidental contact. We know the Norse established some winter camps in Newfoundland around 1000 CE that only lasted year or so. They had more long-term settlements in Greenland that lasted until the early 1400s, which allowed for more regular contact with the Inuit of Greenland.

We know Polynsians and people from South America interacted, probably sometime around the 1200s, but we're not sure of the specifics in this case. The main evidence for this is the spread of sweet potatoes from South America through the South Pacific at this time, along with Kichwa / Canari word for the plant being adopted throughout Polynesia ("kumara" or some variation on that; it's "kumula" in Hawaiian, for example). Genetic evidence from Easter Island also shows that the people there have notable pre-Columbian Native American ancestry.

In the Pacific Northwest, we have historical examples of Japanese washing ashore (including, most famously, a case in which three Japanese sailors survived the storm-tossed crossing and end up as slaves in North America). It's possible something like this could have happened in the pre-Columbian past, but we don't currently have strong evidence for it. A Chinese-style belt buckle has reportedly been found a pre-Columbian site in Alaska, but we're still waiting on details there too. In the mean time, we know that there was extensive and regular contact between people on both sides of the Bering Strait, that only stop temporarily due to the Cold War. Even after Beringia flooded and cut North America and Asia off by land, people still had boats and kept crossing back and forth.

Of course, these incidental interactions between the Americas and the rest of the world, though, didn't have the long-lasting impact that the Columbian Exchange did.

Was there really nothing going on in the Americas?

This is a separate question entirely. Regardless of the Americas' level of interaction with the rest of world, there was a lot going on internally. Without written records, we currently known less about these events than we do for contemporary events in Europe and Asia.

There's no way I could adequately cover the entire history of the Americas in the limited amount of space of a Reddit post. Feel free to narrow down the topic if you want to know what was happening in the Americas at a particular time and place. In the meantime, you may be interested in this post about some of the things going on the Americas in the 1st Century CE. I give a quick overview of the Hopewell there, which were the dominant culture of the day in the Ohio and Mississippi river valleys.