This article implies that it is possible to add new fonts without jailbreaking. I have not tried this method myself, so "your mileage may vary."

The article states that the method works with the current Kindle eReaders and the older ones that support KF8 format eBooks. I believe this includes your 6th generation Kindle (aka Paperwhite 2)

I understand it is possible to add new fonts without jailbreaking as follows:

1. Remove DRM from Kindle files and make them convertible
2. Convert Kindle eBooks to AZW3 file with Calibre and embed the font in the Kindle file
3. Transfer the converted files to Kindle

There's additional details at this article. The article states that the method works with the current Kindle eReaders and the older ones that support KF8 format eBooks. I believe this includes your 6th generation Kindle (aka Paperwhite 2)

I have not tried this method myself, so "your mileage may vary."