15 Year Plan for Retirement: Question

[Toby Jurging]

Hello, first time poster.  Currently working on first flip with a couple of partners.  

Along with investing for flips, I am looking to build portfolio with SF units.  Looking for 1 purchase each year for 15 years, then refinancing them inorder, cashing out and supplementing retirement.  

Question is, has anyone else used this method? If I use the BRRRR method up front to free up cash and re fi at 15years, then mortgage will be greater than revenue. Could finance for 30years, lower payment and then use cash flow to add to principle. Goal is 15 years, so looking for any input if people have done this prior.

Thank you for your assistance