The most common and most likely answer to this crossword clue is the 15 letter word INSTRUMENTATION
I've seen this crossword clue in Financial Times
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Buddy explains!
The straight part
We know that "Arrangement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case arrangement = instrumentation.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 INSTRUMENTATION mean?
INSTRUMENTATION noun- The act of using or adapting as an instrument; a series or combination of instruments
- The arrangement of a musical composition for performance by a number of different instruments; orchestration; instrumental composition; composition for an orchestra or military band.
- The act or manner of playing upon musical instruments; performance
- On a vehicle, dashboard gauges monitoring engine functions and performance, along with other essential functions.