Crown of the Empire (UP)

The achievement should pop in level 18 unless you want to grind it earlier by replaying levels. The chests provide a plethora of resources so make sure to open them at your first opportunity. No resources are needed to open them.

Level 11 has 6 chests
Level 12 has 1 chest
Level 13 has 3 chests
Level 14 has 3 chests
Level 15 has 1 chest
Level 17 has 2 chests
Level 18 has 4 chests