Well it would seem that there are 15C programs out there.
Of course any of the programs for simple RPN machines with keycode programming would work.
Take a look at the following calcs and search for their programs:
HP 34C
HP 25
HP 11 and 10
HP 65
HP 67
Granted there are built in function differences but these can be converted easily to the 15C requirement.
I use the 15C in my shirt pocket for a suite of aviation related programs and it always gets looks from the other crew.
Also, if you were at HCC2010 I had one of the 15C's flashing in the display, with the use of NNN:
"Hello PPC"
I got the description of the program, synthetics and NNN's from Eric Smiths site in which he cites Allen F Tennants, "Synthetics on the HP 15C"
Synthetics on the HP 15C
Cheers, Geoff
Edited: 13 Oct 2010, 2:59 a.m.