imo it's more complicated than any 5 or 6 i've done.
on the other hand, i've seen that people made it with 2-3 lines of code, when i have some spaghetti horror that took me few hours to make it work.

when you try the test, there is info "Completed in ..."
under the window where you put your code there is sample test. you can change it, for example type some big prime number instead of existing prime. you will see how long it takes when you run the test.