I realize that this question was posted a year and a half ago. However, someone else may find the info useful.
I just bought the 20-inch spiked collar (though in store it is the Petco brand rather than the Circle T).
My dog's old collar was approximately 19 inches. But the one I bought, while marked as 20 inches, was actually a bit longer that.
The one I bought has three holes. There is some room to make new holes if necessary.
I do not know if the collar I bought was marked wrong or not. Nor do I know (as I did not check the other sizes) if the other sizes are also somewhat longer.....which would not be the case if mine happened to be marked wrong.
All that being said, I would think that the 18-inch collar would work for a dog with a 15-inch neck.
However, if other folks with a dog that is not yet fully grown are thinking of getting one of these collars I would suggest waiting until the dog has stopped growing as you don't want to pay a lot of money for a good leather collar that the dog will likely out grow.
answered 10 months ago
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