Changes for some collection type achievments

Some achievments in the game require you to level creatures up to a level you most likely won’t need them, resulting in a waste of both coins and DNA, so here’s my suggestions:

Cenozoic Specialist: instead of having Brontotherium, Elasmotherium and Woolly Rhino at lv. 20 lower the level at 15;

Thagomizer: instead of having all the stegos to lv. 20 lower it to 15;

Distinctive Gait: instead of having Amphicyon, Andrewsarchus and Megistotherium at lv. 20 lower it to 15;

Battle Chops: instead of having Archaeotherium and Entelodon at lv. 20 lower it to lv. 15.