I still use my 15C, and I fully agree with your sentiments on RPN. Much easier to use.
On another topic, none of the kids in my Calculus class had ever seen a slide rule until I brought my Post in.
Once, just after my TI calculator died, I was doing a geophysics problem set, in a lab where a bunch of us would study after hours. I was using my slide rule, and the younger students kept asking about it, saying how their dads used to have one and so forth. I ended up giving slide-rule lessons for much of the evening.