user: Question: How many kills have 15 as the injured, with a year prior to 1987?
Columns: ['Perpetrator', 'Date', 'Year', 'Location', 'Country', 'Killed', 'Injured']
Types: ['text', 'text', 'real', 'text', 'text', 'real', 'text']
Sample row: ['Grachev, Peter', '07.31 July 31', 1925.0, 'Ivankovo', 'Soviet Union', 17.0, '03 3']
SQL:

assistant: SELECT SUM("Killed") FROM "Table" WHERE "Injured" = '15' AND "Year" < 1987.0;