EXCLUSIVE

Octomom has been HOSING taxpayers by illegally collecting welfare ... and now we know how much she nabbed.

TMZ broke the story ... the L.A. County Dept. of Welfare Fraud prevention seized Nadya Suleman's financial records, after getting a tip that the mother of 14 was collecting gov funds, despite making more than $200,000 in 2012.

FYI -- Octo can only collect welfare if she rakes in less than $119,000 a year.

Here's what we now know:

-- From Jan. to May 2013 she got $6,666 (appropriate #, right?) she had no right to collect

-- From Jan. to May 2013 she got $9,016 in Food Stamps she shouldn't have gotten

All totaled = $15,683.00 (that's just for 4 months).