pre_text: American Tower Corporation • 2019 Annual Report Appendix 1 • Letter to Stakeholders RECONCILIATION OF ADJUSTED EBITDA TO NET INCOME ($ in millions. Totals may not add due to rounding.)
table: 2015 2016 2017 20181 2019
table: Net Income $672 $970 $1,225 $1,265 $1,917
table: Income tax provision (benefit) 158 156 31 (110) (0)
table: Other expense (income) 135 48 (31) (24) (18)
table: Loss (gain) on retirement of long-term obligations 80 (1) 70 3 22
table: Interest expense 596 717 750 826 814
table: Interest income (17) (26) (35) (55) (47)
table: Other operating expenses 67 73 256 513 166
table: Depreciation, amortization and accretion 1,285 1,526 1,716 2,111 1,778
table: Stock-based compensation expense 91 90 109 138 111
table: ADJUSTED EBITDA $3,067 $3,553 $4,090 $4,667 $4,745
table: Divided by total revenue $4,772 $5,786 $6,664 $7,440 $7,580
table: ADJUSTED EBITDA MARGIN 64% 61% 61% 63% 63%
question: Analyse this data from a financial earnings document. What was the percentage change in Interest expense between 2015 and 2016?