You really need a source for this, and to tag far more. Consider 20 tags the minimum, here. Without source or tags, it cuts the odds of approval significantly, even if people like the work.
Where are you getting that "20 tags" number from? You've been throwing it around a lot in comments lately, but it isn't mentioned anywhere in howto:tag. So long as the Level 0 requirements of howto:tag checklist are met, there has never, to my knowledge, been an official policy mandating a given number of tags. And I'm not sure how you could even enforce such a rule on a regular basis, considering the existence of text_only_page, still life, and other such images where there are naturally very few things to tag.
Where are you getting that "20 tags" number from? You've been throwing it around a lot in comments lately, but it isn't mentioned anywhere in howto:tag. So long as the Level 0 requirements of howto:tag checklist are met, there has never, to my knowledge, been an official policy mandating a given number of tags. And I'm not sure how you could even enforce such a rule on a regular basis, considering the existence of text_only_page, still life, and other such images where there are naturally very few things to tag.
It's a good general baseline goal for most images. Saying "Level 0 tags" doesn't necessarily give a good measure since, as you say, that number can change, and if the problem is users don't recognize and aren't willing to read the guidelines, then giving them a more direct and simple guideline is preferable. Yes, text_only_page exists, and there are some other reasonable exceptions, but text only pages should be really, really rare. (And even in landscapes, tree and house and cloud are all tags...) My typical post has something in the 30-50 range of tags, and in reading other janitor's feedbacks to other users, they often say something like "you should aim for at least 15 general tags" (meaning tags that aren't the copyright, artist, and characters). Hence, to boil it down as simply as possible, a 2girl multi-panel comic page like this should be capable of hitting 30 taggable things easily, and so setting a goal for 20 total tags is a fairly easy baseline that should get users to think of at least the most obvious (level 0) tags.
(And I've said to some users a number like 30 was what they should aim for, minimum, in that post, although that was in images with 4 or more characters...)