Hello from a fellow C Springs Leaf!
I have made a number of trips to the Denver area and beyond in my '15 S with QC no problem. I have posted about some over in the Regional->Mountain States area of this site if you're interested, but I'll recap some more here:
Keep in mind I live near Interquest and I-25, so if you're further south take that into account.
In reasonably warm weather I have driven as far as Louisville a number of times, 82 miles, and have between 17-22% remaining. I have driven to Canopy parking at DIA, 71 miles, with 22% remaining. And to LoDo or Denver museum of Nature and science, 58 miles, I'll have around 50% remaining. This is all in 50-80F whether, little wind, no heat, occasional AC. Haven't nor will I try in winter conditions.
On the way north, relax, drive the speed limit even (on the flats/downhills)! I take monument hill and the hill after castle rock at no more than 60-65, but other than that I keep it between 70-75 for the most part (top speed 80 downhill), even when going much further than Castle rock, so you'll have no problem getting there. Through Denver I keep to the speed limit or 5 over (which still feels slow in Denver traffic).
The way back from Castle rock you'll want to be a bit more conservative, go 65 for the most part, take hwy 83 or 105 if you want a more scenic traffic free drive and you'll save even more power. I usually use about 50% SOC from castle rock to the north end of the springs (33mi) if I keep to 65ish in good weather. I always drive in B mode and no ECO. ECO does nothing for you but I like to use B mode so I have full regen available if bad traffic appears. The trick is just to modulate the pedal to stay near the neutral bubble as much as possible. I try to keep to no more than 3 or 4 bubbles of power up the hills more so than going for a specific speed.
I usually charge at one of the QC's at the south end of Denver for the return trip, not that that applies to you if you're charging in castle rock.