I average about 10 or 11 days per level, but it concerns me that the OP is level 4, so might be talking about levels 1-3, which are meant to be shorter (I finished all three of them in a hair over two weeks, never mind two weeks per level).
@Leebo’s advice about going at the pace that works for you is solid. To an extent, WK is designed to prevent you from going too fast (and therefore not retaining anything, which is something I’ve learned the hard way with another language I don’t speak because I “studied” it too quickly), but there’s nothing particularly wrong with going even slower if you find that more helpful.
I say ‘if’ because the theory behind SRS is that the best time to review something is when you’re about to forget it. That length of time does differ from person to person (and from item to item, for that matter), so WK’s one-size-fits-all timings might not necessarily be the timings that work for you, but if you go too slowly for your own memory, chances are you’ve already forgotten it by the time you review it. That’s not the end of the world either (it’s a rare review session where I can remember everything that comes up, and mistakes are nothing but an opportunity to become more familiar with the item), but if you find you have real difficulty remembering a lot of things, you might want to do your reviews more often.
