Hello, My name is ***** ***** I'll be assisting you. I'm sorry you're having problems.
The Kindle needing to be charged so often is either due to the battery needing to be replaced (most likely) or the device needing to be rebooted (least likely).
I would suggest trying the reboot below FIRST, then if the issue persists - replace the battery (which I will post in a link below the reboot):
The problem you're having is often due to the software in the Kindle locking up and it needing to be rebooted. To do this, simply press and hold the power button on the Kindle for 40 FULL seconds, then release and wait a full minute for it to reboot (do no press anything else within that minute). If this does not cure the issue, try that reset up to THREE TIMES and wait the full minute to reboot and see if you can get more than 15 minutes out of a full charge.
If the reboot doesn't help, then you will want to replace the battery which can be purchased at the link below:
Let me know if you need further help. Also, please do click a 3-5 STAR rating for my efforts before you go. That is how I am credited for my efforts by the site.
Please keep in mind rating me does not close the question in any way- it simply ensures I am paid for my time spent trying to help you. You can follow up at any time at no additional cost.