There are many ways to learn to code these days. From coding bootcamps like Flatiron School to online courses to totally free beginner resources. The best way to learn to code depends on many factors, but the most important one is you. See what course is best for you.
In the real-world applications, there should not be any case where you need to get 15k rows without any kind of filter.
Also very long reports usually do a sort of "paging" on data.
That's all.