The most common and most likely answer to this crossword clue is the 12 plus 3 letter word HYDROGENATED FAT
I've seen this crossword clue in Independent
H
Y
D
R
O
G
E
N
A
T
E
D
F
A
T
Buddy explains!
The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.