For reference, I did two years of Chemical Engineering and I plan on switching to Computer Engineering this semester. In order to graduate on time, I’ll need to take 4 more semesters of 19, 18, 18, and 15 hours. I am an out-of-state student on a full scholarship, so I would rather not pay for an extra semester (~20k). I don’t need to work at all, have no commute (live 5 minutes away by walking), and have basically zero other responsibilities. There is also the issue that future semesters will likely have tougher classes, but I can face that when I get there. I had a 4.0 in ChemE after 2 years. For example, this is my schedule for the coming semester:
Digital Logic Circuits (3 hours)
Circuits I (4 hours)
Intro to OOP in C++ (4 hours)
Discrete Math (4 hours)
Engineering Statistics (3 hours)
Physics Lab II (1 hour)
(19 hours)
Although I am more concerned about later semesters where I will have 3-4 upper div EE/CS courses with 1-2 EE/CS electives…
For reference, here are my last two semesters of chemE (4.0 in both).
Last:
Organic Chemistry II (4 hours)
Organic Chemistry Lab (1 hour)
US History (3 hours)
Differential Equations (3 hours)
Thermodynamics (4 hours)
Intro to C++ (3 hours)
(18 hours)
Second to Last:
Organic Chemistry I (4 hours)
Calculus III (4 hours)
Physics II (4 hours)
Physics Lab I (1 hour)
Process Principles (3 hours)
Honors WWII History (3 hours)
(19 hours)
Any thoughts? Is this doable? Should I just give in and take the 20k in loans?
No one on an anonymous internet forum is really in a position to determine what you can and can’t do. 
Looks like you’ve been holding down a 4.0 while taking 18-19 credits, and classes like Organic Chem II and Thermodynamics are not that much easier than your upper level classes, so no reason why you can’t continue on your plan. Your advisor at school should be able to let you know if this may be an issue.
Worse case, you end up having to drop a class along the way and need to take that extra semester.
Also, talk with your advisor about other options, incase you do run into problems. For example, can you take some classes at a school that’s in-state (or on-line), over the summer? Sometimes they will let you take a class at another institution, but they will have several restrictions. It’s worth researching now, as it means you may want to push some electives to “next summer”.
Another option is study abroad over the summer (or in the fall/spring), to keep you on track to graduate in 4 years. If you’re going to end up spending $20K for an extra semester, maybe it makes more sense to spend that money to study abroad and still graduate in 4 years (or take the “extra” semester overseas). For example, at Georgia Tech, out of state students pay in-state tuition rates when doing a study abroad (and GT has GT faculty, teaching engineering courses in France, etc.).
Finally, make sure you’re doing something other than just attending classes! If nothing else, join one of your school’s computer engineering student organizations/clubs (ACE, ACM, IEEE, etc.). Attend some meetings, go on a few site visits and so some networking. Try to get something on your resume other than classes and GPA.
Good Luck!