It sounds like you are building too fast. You have to give your city time to grow and mature. As building gain levels, they evict the current residents and call in more off-map citizens, and they do this over and over. So, you'll have a lot of traffic early on. Once you have maxed your building's levels. Then traffic will subside and be normal. but during grow stage, you get a lot of traffic. Try creating temporary on/off ramps along the highway to get cims in and out of your city easier, then remove them after your area matures.
As for realism. How many cities have you seen grow from zero 15k in a few short years? They grow gradually over time. Not all at once. You are just getting an artificial effect right now, as this doesn't happen in real life. To prevent this, I always play at x3 sxpeeds so building will level up faster and trafficx subsides quicker, while I build somewhat slow and steady.
Lastly, you'll need to balance out your city as it grows as well. If you have too many or too few workers (residents), then you will export/import workers, causing more issues. Same with industry, if you create excessive or too few goods, then you get goods being imported/exported and generating excessive traffic. Also, if you build your RCI zones too far away, then you get excess traffic from everyone making long trips everywhere. i.e. to work, shopping, delivering goods, importing goods because goods are too far away so they import them. Delivery distances are very short. less than 1km.