Useful new systematic test figures on durability for your old CD-Rs and DVD-R burned-media archive discs.
“Surprisingly, with no special storage precautions, generic low-cost media, and consumer drives, I’m getting good data from CD-Rs more than 18 years old, and from DVD-Rs nearly 16 years old. Your mileage may vary.”
So it looks like 15 years can be more or less counted on, provided they’re stored out of sunlight and in a dry place. Still, it might be best to get the stack out and then systematically go through and copy off still-wanted items onto an external hard-drive.