I mean, really, why would it be encrypted?

[Koen G]

Would the VM be perceived (in the 15th cen.) as an encrypted text or an exotic language text?

It depends who's doing the perceiving, I guess. An experienced reader in the 15th century would recognize most of the characters as common ligatures, abbreviations, numbers... So my guess is that they would think someone's been messing around rather than it being some genuine foreign script.