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.
Making A Cheap 15mm Spanish Village
Lead Gardens offers a tutorial on making cheap 15mm spanish villages.
Painting 15mm Horses Tutorial
Anatoli’s Game Room has a tutorial on painting 15mm horses.
15mm WWII German Propaganda Posters
The 15mm Paint Shack has a couple of pages of German propaganda posters scaled for 15mm. You can print these and use them to embellish your WWII terrain.