The most common and most likely answer to this crossword clue is the 15 letter word UNSUBSTANTIATED
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More clues leading to the result UNSUBSTANTIATED
Buddy explains!

The straight part
We know that "wanting a fact check?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wanting a fact check? = unsubstantiated.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 UNSUBSTANTIATED mean?
UNSUBSTANTIATED verb- To prove false; to disprove or discredit.
- (human services) To officially categorize (an allegation) as unsubstantiated.
- To call into question; to create doubt about.
- To make insubstantial or abstract; unsubstantialize.
- Lacking substantiation; without evidence.