Find rows where any column matches a search pattern
Well, there is the plain and simple "brute force" way:

SELECT *
FROM   "Test"
WHERE (col1 LIKE '%ABC%' OR
       col2 LIKE '%ABC%' OR
       col3 LIKE '%ABC%' OR
       ...
       col15 LIKE '%ABC%');


Parentheses won't be necessary if you don't have additional WHERE expressions. 
Probably faster (and more robust in any case) than concatenating all columns for a single LIKE test.