I've never taken more than 15 hours in a semester, and that was only once. I usually only take 14, and I'm currently underloading this semester (10 hrs; I only need a 1 hr PE class to graduate), and it hasn't been a problem at all during the admissions process. I had 26 hours worth of AP credit (basically a year's worth of classes), so I've never had to take more to graduate on time. To be fair, the semesters where I've only had 4 classes, a majority of them were science classes. But it's never come up as to why I didn't take a more strenuous course load. If you can take it easy, I don't think it will be a problem as long as you do well.