You really need to talk to a mortgage broker and have them run a spreadsheet for you to see if a re-fi will actually save you money in the long run. We own a rental, and rates on rentals are higher than on primary residences. You're probably looking at a rate of 3.75%, vs the 3.35% that everyone else is getting on primary residential purchases.
The real question is, if you have a loan at 3.75%, how much interest will you pay at the end of 15yrs vs paying 4.65% for the next 10yrs. adding 5 yrs to a loan is a lot of interest.