Yeah it would help if we know your specs, otherwise we're not sure if it will run on your PC. Some PCs might not be able to run it at all. There's also a site called "Can you run it" which allows you to check your PC specs and they'll check if any PC games will work on your pc. It helped me find what games will work and won't work on my PC.
Firstly, you should set the graphics and fps settings according to your computer specifications and secondly , you should make sure that other apps are close before opening the game so that Fortnite gets enough attention from the RAM.
Its depends on the laptop. I have a gaming with GTX 1060 graphic and a normal laptop ( i5 4th gen 8 GB ram ). I can smoothly play games on my gaming laptop but its lags on my i5 laptop. What's your spec can you list it here ?
I think 4GB of Graphics Card and the 16GB minimum RAM is more than enough for playing high end games. You need desktop configuration that gets you closer to those sort of the box. I'd also say that you should upgrade if your processor is i3 or Athalon AMD. Instead you should be making use of the Ryzen 5 and the i5 minimum processor.