Two Page Tricorn is a set of rules for 18th century warfare. It is designed for the quick resolution of large scale battles, ideally using 6mm figures.
15mm
Making a 15mm Graveyard
Here’s a tutorial on making a graveyard for 15mm scale figures. It could easily be scaled up, though.
Making 15mm Hedges
Here’s a tutorial on making a 15mm hedges.
Restless Natives Colonial Rules
Restless Natives is a set of free wargames rules for playing wargames in the colonial period. They’re intended for 15mm figures, and use a card-based movement and special events system.
Painting 15mm Zombies
Given the fact that you need so many of them 15mm is the perfect scale for Zombie games. Here’s a tutorial on painting them.