Rigged models cause insane lag, am I doing something wrong?

I wanted to make an animated character for the first time. I've made a model of a human in Blender with around 100 polygons, I exported it in fbx. I can copy thousands of them into my scene and the framerate is still around 150. Then I made armature for my model and suddenly one instance is enough to reduce FPS to 45, removing the skeleton removes the problem, but I need animations. Did I make any mistakes in Blender? I just made a few bones, parented the model to them and used weight brush, then I exported armature and model together.