Early retirement investment strategy

[Johnny Horner]

BP community, help me settle a debate with a colleague, here is the scenario:

We have a friend, let's say his name is Bob, he would like to leave his w-2 job. Bob, mid 50s, currently has 20 doors averaging $450 cashflow a month, 9 grand total. Let's say around 1.5 million in equity. Portfolio comprised of SFR with a couple small multifamily. He would like to reach $15,000 CF a month in next 2 years, what is his best strategy to achieve? Thanks in advance for the input.