Final answer:
The text does not provide the exact percentage of total sales revenue that U.S. corporations generated in 2015, as it mainly discusses the corporate income tax receipts as a share of GDP over the years.
Step-by-step explanation:
According to the information provided, U.S. corporations' contributions to total sales revenue are not directly mentioned in terms of percentage for the year 2015. Instead, the text discusses the share of GDP (Gross Domestic Product) that corporate income taxes accounted for historically. Throughout the years, corporate income tax receipts have shown a decline as a share of GDP, with about 4% in the 1960s and averaging 1% to 2% of GDP in the past 40 years. For a specific percentage of total sales revenue generated by U.S. corporations in 2015, additional data from the source would be required.
It is important to distinguish between tax contribution as a share of GDP and total sales revenue. Thus, without explicit data on total sales revenue for corporations in 2015, the question cannot be answered based on the provided excerpts.