Sounds like you had a great summer. I also started out my fixed lined fishing career using a crappie pole. As with you I had alot of fun and caught alot of fish.
When fishing still waters, I fish a 21' furled line and a 9-10' two or three step tapered leader/tippet (total lenght about 30'). IT is nice to have the extra reach. It does take a bit more concentration to cast. I don't use such a long rig when fishing streams/rivers since I can usually get a little physically closer to the fish.
When fishing your nymphing set up, I'm not sure you need a furled line, you might be better off with single strand mono or flouro. At least from my experience, by the time you add multiple weighted nymphs, split shot, indicator, ..., you have enough mass in place to effectively chuck and duck. It may come down to a question of how much mending you may need to do, being able to elevate most or all of your line should eliminate the need to do too much mending. Just a thought.
I have found that actual tenkara rods are at least as tough and robust as a crappie pole. The tenkara rods tend to have a bend don't break design philosophy. Of course if you add enough force to any rod, it's going to fail which is why you want to make sure you have a weak link in place, i.e. a tippet. I did have a tenkara rod fail this spring. My wife and I were fishing for trout early spring. My wife got her leader/tippet tangled into a ball, so I took her tenkara rod and gave her mine. I was in the process of preparing a new leader, and had her rod under arm, line dangling in the water. As Luck would have it, for some reason I had just took the rod in hand when a steellhead grabbed the dangling fly. It too straight to the air, I instinctively lowered the rod when the fish jumped. He pulled the lilian off the end of the rod, taking my line with him. No damage to the rod other than having to epoxy on a new lilian. Had it hit a second earlier while the rod was still under my arm, I'm convinced I probably would have lost the entire rod. All in all, it was a memorable experience.
I don't think I could personally handle a 15' rod. It's not so much the weight, but that's a long lever arm to try to handle with one hand since there is no reel to act as a counter balance below your wrist. I think I'd have to experiment with some two handed spey tenkara techniques.
I do agree with you, it is a fun way to fish with plenty of room for experimentation.