Are you asking whether you will have to pay tax on the gain on the new home when you sell it in 2019 or 2020? If you own and live in the new home for at least 2 years before you sell it, and the gain is less than $250,000, you will not have to pay tax on the gain. I assume you used the exclusion of gain when you sold your old home in Sept. 2015. But the sale of the new home will be more than 2 years after the sale of the previous home, so you will be able to use the exclusion again.
HOWEVER - Everything I have said is based on current tax law. Congress is seriously considering major tax reform, so these rules could very well change by the time you sell your new home. There's no way to predict what the rules might be at that time.
