It is the start of my opponents turn, if I am a 2 token on the frozen fortress and they Stupefy the token. Does the token die?

Yes — the token dies.

The Frozen Fortress trigger ("At the start of each player's Beginning Phase, deal 1 to each unit here") goes on the chain when your opponent's Beginning Phase begins, and your opponent can play Stupefy in reaction. Since Stupefy has Reaction, it stacks on top and resolves first: the token drops from 2 Might to 1 Might (Stupefy's floor). Then the Fortress trigger resolves, marking 1 damage on the token. Damage equal to its Might kills it at the next cleanup check (FAQ #10599).

Even if the order were flipped (Fortress damage first, then Stupefy), the result is the same — damage stays marked, and once Might is reduced to 1 with 1 damage on it, the token dies.