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Charlie Sheen 's ex-wife Brooke Mueller is banging down his door, ready to collect on the huge bill -- about $15 million -- she claims he owes her for unpaid child support.

Brooke informed an L.A. County judge she wants Charlie to cough up the money ASAP. In docs filed Thursday, and obtained by TMZ, she says the ex "Two and a Half Men" star owes her $8,967,600 in child support plus another $6,418,643 in accrued interest.

And, the kicker ... mama wants it paid in full in 30 days! Gallery Launch Gallery

Brooke explains Charlie was ordered to pay her $55,000 per month in child support in April 2010, and there were no issues until July 2011 ... when he started sending either partial payments or failed to make any payments at all. So, she wants the court to make him pay w

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