Let me start by saying I'm no expert by any means! But I am in a similar position I have recently rented out my primary residence after moving in with my gf . From what you said it sounds like you would like to get into rental properties and are willing to make some sacrifices to do it. I think it would be much easier to just buy a second property and rent it out especially if you could make it cash flow . The only reason I would see you needing to go through all the trouble of refinancing again is if you needed the money for the down payment in the long run leaving the 15 year mortgage saving for 2 years and buying a second house as rental would probably be best and my guess is the market will be a little softer in 2 years and if the market does go down in the next few years you could have 2 houses one upside down and with no equity but hopefully still cash flowing but I'm no expert and I live in California where cash flow doesn't exist unless you bought in 2011