Speed is something that generally comes with time, first you need to be able to render accurately, as you get more confident with your subjects and more knowledgeable about them and the materials you use, you'll be able to work faster and more accurately. That said some artists do tend to take longer even after several years, we all work at our own pace. Speed can be good but accuracy tends to be more important.
Anyone can draw a stick figure in a few minutes but not everyone can paint something like the Mona lisa.
And this applies to everything (piano comes to mind for me). Learn it right first, then worry about getting faster. If you try to learn speed whilst still struggling for accuracy, you will end up not achieving the results you could have. Speed comes with time.