What is the percentage change of Revenues from 2015 to 2019? 
{"Statement of Income Data: -- Revenues(1)": {"2019": 2868755.0, "2018": 2815241.0, "2017": 2291057.0, "2016": 1824228.0, "2015": 1851917.0}, "Statement of Income Data: -- Net income, attributable to OpenText(2)": {"2019": 285501.0, "2018": 242224.0, "2017": 1025659.0, "2016": 284477.0, "2015": 234327.0}, "Statement of Income Data: -- Net income per share, basic, attributable to OpenText(1)": {"2019": 1.06, "2018": 0.91, "2017": 4.04, "2016": 1.17, "2015": 0.96}, "Statement of Income Data: -- Net income per share, diluted, attributable to OpenText(1)": {"2019": 1.06, "2018": 0.91, "2017": 4.01, "2016": 1.17, "2015": 0.95}, "Statement of Income Data: -- Weighted average number of Common Shares outstanding, basic": {"2019": 268784.0, "2018": 266085.0, "2017": 253879.0, "2016": 242926.0, "2015": 244184.0}, "Statement of Income Data: -- Weighted average number of Common Shares outstanding, diluted": {"2019": 269908.0, "2018": 267492.0, "2017": 255805.0, "2016": 244076.0, "2015": 245914.0}}
revenue_2019 = df["Statement of Income Data: -- Revenues(1)"]["2019"]
revenue_2015 = df["Statement of Income Data: -- Revenues(1)"]["2015"]
answer = (revenue_2019 - revenue_2015) / revenue_2015 * 100.0