Headers have 3 heads and 4 limbs (arms and legs).
Leggers have 1 head and 6 limbs.

Between all my Glogg friends there were 15 heads and 48 limbs, so we can say:

Number of Heads: Headers × 3 + Leggers = 15
Number of Limbs: Headers × 4 + Leggers × 6 = 48

Solution:

Headers = 3
Leggers = 6

So there were 3 Headers (9 heads + 12 limbs) and 6 Leggers (6 heads + 36 limbs).