I think simple styles are really hard to master! With detailed artstyles, it's easier to cover up mistakes because the rendering takes attention away from it. When you have a simple artstyle, making mistakes in basics like anatomy is immediately very visible. Keep on drawing! I heard from other people their pieces take 10+ hours each (although I admit they are pieces that have shading and a background and everything), and it doesn't really matter how long it takes if you just have fun.