"Why Andrew Tulloch Turned Down a $1.5 Billion Offer From Mark Zuckerberg" - https://techiegamers.com/andrew-tulloch-rejects-zuckerberg/

"according to people familiar with the matter."

aka, made up. They can make up anything by saying that. There are numerous false articles published by WSJ about Tesla also. I would take what they say here with a grain of salt. Zuck himself said the numbers in the media were widely exaggerated and he wasn't offering these crazy packages as reported.

That seems insane - even over 6 years. Maybe he was offered 1.5 billion in funding for the work itself ?