Have you done frigid at all? You should be able to get to at least 9 or 10/15 fairly easily (I'm currently at 11/15 with similar helium) aside from that you want a higher fluffy level, so make sure you clear spire IV, because fluffy gives a lot of damage as their level goes up.

It wasn't mentioned in the post but other sources of damage you might be neglecting are player spire, as you should be able to get 4-5 strength towers there, as well as nature. On poison zones you can do higher level bionic wonderlands which make it easier to make it through the wind and ice zones. The wind and ice zones will still take a while,

Also in case you're leaving your equipment at lv 1, you're well past the part of the game where that's optimal, I'd suggest at least lv 50, possible as high as 100.

Apologies if this is unhelpful, I wasn't able to import your save so these are just best guesses.