Actually, light is incredibly fast, not slow. In fact, it is the fastest thing we know of in the universe. The speed of light in a vacuum is approximately 299,792 kilometers per second (186,282 miles per second).
When we talk about light taking a long time to cross our galaxy or travel between galaxies, it's because the universe is vast and the distances involved are immense. Our galaxy, the Milky Way, is about 100,000 light-years in diameter, which means it would take light about 100,000 years to cross from one end to the other. Similarly, there are billions of galaxies in the universe, each separated by vast distances.
The vastness of the universe and the enormous distances between celestial objects is what makes it seem like light takes a long time to travel. However, in terms of speed, light is incredibly fast, and its speed is a fundamental constant in our understanding of physics.