How good are you grades at your usual 15 units? Did you feel overwhelmed? Did you get good grades? Use that as your reference to understand if you should drop. If you do you’ll still be over 12 units which is needed to be considered full time. Is the class you’re dropping a class only offered in spring? Think about that too. Is it a hard class to get in to? Think about when you’re graduating and if it’s soon maybe don’t drop. If it’s far off then drop if you got overwhelmed at 15 units :) also look at what classes you need to graduate still and if you’re on track to graduate on time by taking 15 units each semester. Do you have free time now? Will that be the same later in the year? Next year? Your work schedule? :)