Could depend on how many courses / credit units he takes. Since a 6 week summer session is 3/5 of a 10 week regular quarter, taking 9 units in that summer session should be a similar workload as 15 units in a regular quarter.
It does look like there are two 6 week summer sessions at UCD: 2023 Courses | Summer Sessions . There is also a summer special session and a full 10 week summer quarter, but those appear to be mostly individual or group study, field work, etc. type of “courses”.