I am trying to print something that might take 15 hours. I don't want to risk my printer so if I print for 15 hours, what is the worst that can happen? So far, I haven't printed anything for more than 5 hours.
As long as your printer is well designed as far as safety and you didn't get one without thermal runaway protection you should be fine. Worse case scenario: you have a big mess to clean up and a lot of wasted filament.
I've printed jobs taking as long as 50 hours over a weekend using a German Reprap x400.
- Used a large enough UPS to support the printer and the computer.
- Printed the gcode file from a USB card instead of the computer, so that a computer update or reboot doesn't interfere with the print. [If you can't print from media independent of the computer, you can disconnect your computer from the network and/or internet.]
Overnight prints still fail sometimes, probably from power issues the UPS doesn't filter out. Often this means the filament material melts all over the hot end instead of sticking to the print on the bed and leaves a mess to clean up.
Other than that, I'm not sure of the risk for your particular printer model.