its not bad at all in my opinion, i've definitely seen far worse. it seems to be a little above average; if i were to ask a random, non-artsy person to draw that same picture i think yours would be visibly better. i'd say its actually really good when you consider that you havent drawn in ages, used a pen, had only 10 minutes, and didn't draw guidelines. i can tell its leo, and making portraits recognisable is harder than people think, so you did a good job overall.
in terms of improvement- sorry if this is unsolicited, but in case you are looking for specific ways to make it look nicer, i'll say it anyway:try to define the nose more. and make sure that if you're drawing visible teeth there's soft shading so that they don't look weird... i tend to avoid drawing teeth for that exact reason that they can easily look strange but that'd be my advice if you still want to. his eyes are looking in just slightly different directions, but that's an easy fix in the future- i always do that once or twice before finally getting them both the same, but you were using pen so i think thats understandable. also there seems to be a little bump(?) in the outline of his face on the side without the hair flick, which isn't too hard to fix.