I'm really confident that it's not NTP causing the problem. The program sends me txt msgs throughout the day, including the time of day to seconds. I've never seen it appear to be out of whack. Doing a 'date' at the command line also seems accurate.

Tell me this - if the command line time on the rPi is correct right now, and I do a 'shutdown -r now', when it restarts, would the time be way (15 mins) off?

I did a vanilla noobs installation - doing a 'ps ax | grep ntp' I do not see NTPD running. This means that NTP is not changing the time under the running program, right? Does linux have some default occasional NTP run that I don't know about?

Thanks for your thoughts!