U.S. nominal GDP was $19.5 trillion in 2017. Annualized, nominal GDP reached $20.1 trillion in Q1 2018, the first time it exceeded the $20 trillion level. About 70% of U.S. GDP is personal consumption, with business investment 18%, government 17% (federal, state and local but excluding transfer payments such as Social Security, which is in consumption) and net exports a negative 3% due to the U.S. trade deficit. Real gross domestic product, a measure of both production and income, grew by 2.3% in 2017, vs. 1.5% in 2016 and 2.9% in 2015. Real GDP grew at a quarterly annualized rate of 2.2% in Q1 2018 and 4.1% in Q2 2018 under President Trump; the Q2 rate was the best growth rate since Q3 2014.

Answer this question based on the article: In which year was real gross domestic product the highest?