The Actual Monterey Installer of 15.72 GB does required that space Plus addition Empty Space to Expand and then installed.
It has been accepted that a Minimum of 50 GB or More Empty Space is a Requirement for a successful upGrade
And Empty Space afterwards - it is suggested to keep at least 15% to 20% of the Drive Total Capacity as Empty Space for good operations of the computer and for additional updates to Monterey to download, expand and install.
There has been enough advise / suggestions offered for the User to make an informed and educated choice what the next course of action is required.
The suggestions have been put forth on a volunteer basis, in good faith and in the best interests of the computer.