Capable, fifteen working around Channel Islands (9)
I believe the answer is:
efficient
'capable' is the definition.
(I've seen this before)
'fifteen working around channel islands' is the wordplay.
'working' is an anagram indicator.
'around' is an insertion indicator.
'channel islands' becomes 'CI'.
'fifteen' anagrammed gives 'effient'.
'effient' enclosing 'ci' is 'EFFICIENT'.
(Other definitions for efficient that I've seen before include "Capable" , "Effective in doing what is required" , "Effective, competent" , "Performing with little wastage" , "Producing results with little waste of effort" .)