Working with live animals, one doesn’t get many guarantees.
1 male to 15 has worked here, as have 1 to 2, 1 to 7, and many more. Age and time of year also play a role in this.
Young cockerels here are much more hormone driven, as are males during the breeding months. Males will also pick favourites, that’s usually 1-3 females, but will gladly accept more.
It is definitely possible that you will need to get more females, but it’s also possible that your current ratio will work out well. Whether or not you would prefer playing it safe (i.e. getting more females now) before/if it becomes a problem is up to you. Make sure to quarantine new birds before introducing them to your current group