Theoretical question, calling all in early

[Philo]

I have a theoretical question about making an all in call early in a sng.

It's early in the tourney, still 10 players left. Blinds are 10/20, you've got 1,500 chips. Hand is folded around to SB, who goes all in for 1,500.

Suppose by chance you get to see the SB's cards. Question: what percentage favorite would you have to be to call the all in here, and why? Does it make a difference what the buy-in was?