"""Substitutes placeholders in a template string with corresponding values from a dictionary.

The function performs the following steps:
1. Deep copies the input dictionary to avoid modifying the original.
2. Modifies specific keys ("KernelSchedule" and "EpilogueSchedule") by prepending "collective::" if they contain the substring "Auto".
3. Iteratively replaces placeholders in the template string (formatted as `{key}`) with the corresponding values from the dictionary until no more substitutions are possible.

Args:
    template (str): The template string containing placeholders to be replaced.
    values_base (dict): A dictionary where keys correspond to placeholders in the template and values are the replacements.

Returns:
    str: The template string with all placeholders replaced by their corresponding values.
"""
You should write code starting with:
import re
import copy

def SubstituteTemplate(template: str, values_base: dict) -> str:
    # TODO: Implement this function
    pass

