Caitlin Clark was slated to make AT LEAST $15 million if she had agreed to suit up for Ice Cube's Big3 ... so says league co-founder Jeff Kwatinetz, who's revealing more eye-popping details on the lucrative offer.
TMZ Sports broke the story ... the former Iowa basketball superstar was presented a historic $5 million deal to play just 10 games for the 3-on-3 organization last month -- while still being able to pursue a WNBA career.