From the bank’s website:
“Prosperan is a form of the word ‘prosper.’ It means to be successful or fortunate, especially in financial respects, to thrive and flourish. In Spanish it means, ‘all of us prosper.’ It communicates prosperity, growth and security and has an open meaning that allows it to be equally effective, engaging and communicative throughout the United States.”
Related article here.
This name resembles other players in the financial industry, Prospera Credit Union in Canada, Prospera Credit Union in Wisconsin, and Prosper.com, the peer-to-peer lending site.