The most common and most likely answer to this crossword clue is the 15 letter word UNSOPHISTICATED
I've seen this crossword clue in The Guardian
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More clues leading to the result UNSOPHISTICATED
- Simple duties can, mixed with this absorbing work
- Low-tech Dictaphone suits criminal
- Simple decision that’s up for review
- Simple duties can, when mixed with this absorbing work
- Green sauce in pot, dish stirred around beginning to thicken
- Green, coup d’état his sin, taken out
- Simple Harry Houdini act with steps
- Crude or rough depiction as thus?
- Plain and pistachio nuts ordered by editor
- Stupid action she condemned as naive
Buddy explains!

The straight part
We know that "Simple" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case simple = unsophisticated.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.
What does UNSOPHISTICATED mean?
UNSOPHISTICATED adjective- Not sophisticated; lacking sophistication.