Correct spelling, explanation: turkeys is the correct plural form of turkey; to create a plural form of words ending with y preceded by a vowel we just add s at the end. If y is preceded by a consonant, y is transformed to I to which we add -es. In this case, turkey ends with ey, so with a vowel before y. This is the reason for the plural form to be turkeys. Therefore turkies is incorrect.

Definition of turkeys:
noun, plural form of turkey, a big bird of domestic poultry; (note: Turkey is also a name of the country in West Asia, however, it has not got a plural form)
My grandma keeps some turkeys at her farm.
I don’t like chickens. Turkeys are much tastier.

Incorrect spelling, explanation: this form is mistaken because to create the plural form of nouns we ass s at the end. There are a few exceptions, and one of them is the case when a word ends with y with a consonant before it (y is then transformed to i). However, here we have a singular form turkey, so y is preceded by e, which is a vowel. Therefore the correct plural form is turkeys, not turkies.