A bit of background:

I'm now a freshman about to complete my first semester at a pretty reputable college in the US. I'm majoring in a pretty high paying STEM field, and I come from a family that is well off. However, my parents are paying $45k per year for my college tuition.

I feel a bit guilty for the financial burden that I'm putting on them. If I take 16 - 18 credit hours each semester, I will definitely be putting myself under a bit more stress than normal, but I'll also end up graduating in 3 years. Additionally, my grades might be marginally worse. I'm currently taking 15 credit hours (not counting bs classes) and I am not struggling at all. I have 18 planned for next semester.

However, if I take my time, I will graduate in 4 years, which a better GPA, and I might enjoy my college experience a bit more. (I'm already having a great time, so I'm not depressed or extremely overworked or anything.)

Any advice on what to do?