Digitimes is the originator of this rumour.
Of course, that means it's completely incorrect. What is more likely is they have misinterpreted news that Foxconn will be building 15" MacBook Pros as a supplementary supplier to Asus and run with the news as "Foxconn to build 15" MacBook model" - if we're to believe Digitimes then the G5 PowerBook and G5 iBook models are now over a year late, and they were dead certain Apple were going to release them.
And besides, there's really no room in the line-up between the BlackBook and the MacBook Pro for a 15" MacBook.