Number of clusters 'k' must be in {1,2, .., n-1}; hence n >= 2", is displayed.

General
2

Please make your example reproducible. ( object 'count_15_lv' not found etc.)

You can test to see if it would be , by pasting what you propose to post into a blank new R session, and seeing that it does what you expect.

Here is general advice on how to make a reprex;