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