In 2014, Barry Hughes, 38, was fined for illegally obtaining £1,287,955 for two mortgages, and laundering £150,000.
At Glasgow Sheriff Court on Monday, his QC Gordon Jackson said Hughes had offered to repay £500,000 to bring the matter "to a complete end".
He told the pre-proof confiscation hearing the Crown claimed the "benefit figure" from Hughes' crimes was £5.9m.
But he warned if the proof hearing went ahead as planned, it could take up to six months.
The defence counsel said: "Standing the way the law is we would require all transactions, £5.9m which have gone through his account and have to be spoken to, challenged or whatever."
Mr Jackson said it was up to the defence to prove that all these transactions were legitimate.
He said: "There are about 1,500 transactions for which evidence will require to be led, allowing 20 minutes per transaction one can begin to calculate.
"The estimation, I'm horrified to say to you, is over 150 court days."
Mr Jackson said he did not think the Crown would accept Hughes' £500,000 offer "in the hope presumably of getting something else more in the future which they will never get".
Sheriff Paul Crozier continued the case for another pre-proof hearing and urged both sides to adopt a "mature and realistic attitude".
Hughes was jailed in March 2013 for 43 months but his sentence was overturned and he was fined £45,000.
He had lied about his wife's income on mortgage applications in 2004 and 2006.
He claimed his wife Jacqueline made £160,000 from her business McDonald Interiors - but divorce papers lodged by her in 2006 stated she was "financially dependent" on her husband.
He also admitted two money laundering charges - for receiving £128,885 after selling the first property and spending £30,000 towards a Rolex watch.
A former boxing promoter who admitted a £1.2m mortgage fraud could lose nearly £6m under proceeds of crime laws.