but after 15 years, i am sure you willnot be able to find any devise where you can put this floppy disk to start, so they would be usless.
take some mini disk and write your wallet.dat and txt file there and put this disk in the safe place. this will be better option
You can still buy external floppy disk drives that plug into your usb port. This one only costs $13.99
http://www.amazon.com/Sabrent-External-Floppy-Drive-FL-UDRV/dp/B00E9MD700/It might last 15 years if you don't use it much. Nevertheless I wouldn't trust a floppy disk to store a wallet safely for a long time. I'd back up a wallet in triplicate on a cd, dvd, and a thumb drive. Floppy disks are from the stone age.