For Bloom and Doom you can use Sunflowers to slow down the zombies and potentially get 3+ waves without having to leave the game
3 waves was my best, though I guess you could get more with 5 lawnmowers, Sunflowers are the only plants you can place and still get the achievement in only 15 waves, so don't place anything else.
Just a quick tip that should help speed things up for people![]()