K-15 is a 257.141-mile-long (413.828 km) north–south state highway in the U.S. State of Kansas. Originating at the Oklahoma state line as a continuation of State Highway 18 and continuing to the Nebraska state line where it continues as Nebraska Highway 15. Throughout Kansas, it is signed as the Eisenhower Memorial Highway due to its route through Abilene, where the Eisenhower Memorial Museum and Library is located.

State Highway 18, abbreviated as SH-18 or OK-18, is a highway maintained by the U.S. state of Oklahoma. It was once one of the longest state highways in the Oklahoma road system, but now has a total length of 134.4 mi (216.3 km).