If the students don’t take away actual results, the teachers watching won’t listen to what I’m saying. It works both ways.
We did six years of STARTALK programs (those were 3 weeks long, though) in Hawaii at which students who did a total of 12 hours of TPRS and 10 hours of cold character reading recognized and could read 130 characters (in any context, not just “one story they knew”) and wrote, on a freewrite, between 90 and 310 characters on a freewrite under test conditions, with error rates averaging (I’m recalling here, don’t have the data in front of me) around 1.4 per 100 characters. Those were also “blended” programs where teachers were being trained as students learned Chinese. That’s where I got that model from. It’s reasonably well-known in among people who teach Chinese using CI.
15 hours would be somewhat less in the literacy area of course, especially since most people would prefer to focus on spoken language if it’s just a short course. We also did two 5-hour sessions this summer with fifth graders who read a 400-character long book (with 29 unique Chinese characters) at the end (also understanding the language used in the book in different contexts, in speech).
Are those results? It depends on what you’re looking for, I guess. For NT$1000 it probably isn’t bad.