The most common and most likely answer to this crossword clue is the 3 plus 5 letter word EGG TIMER
I've seen this crossword clue in Financial Times
E
G
G
T
I
M
E
R
More clues leading to the result EGG TIMER
- Grains turned up for breakfast, for a limited period
- Device for boiler say ultimately needing set-up instructions
- Device giving go-ahead for soldiers to penetrate area that's been shelled
- Kitchen device, say – good range, on reflection
- Culinary device, say, Tim and Reg ruined
- 15 device that makes perfect soldiers’ companion
- It’s a feature of kitchen cabinet to incite send-up
- Soldiers at the ready … wait for it!
- You may get cracking in the kitchen after using this
- It helps one who’s boiling mad, initially, interrupting to incite row
Buddy explains!
The straight part
We know that "15 /de/vice that makes perfect soldiers’ companion" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case 15 /de/vice that makes perfect soldiers’ companion = egg timer.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.