Capital Gains on a Rental? (CPA's please chime in!)

[Doug Vigliano]

So I bought a house in June 2015 in Orlando, FL 

I currently have it rented out with an option to purchase, they tenant-buyers put down a fairly large option fee and are self-employed, the deal should close in 2019

I have since moved to Texas and am renting a house.  Since I didn't buy a new house, this is the only "mortgage" on my credit.  

My question is when it closes, will I have to pay capital gains since this is technically my primary residence? 

I guess my question is what qualifies as a primary residence? Just because I've moved if I don't own anything else, does that qualify?