I have the same problem, only get to 98% used space with only installing quick creds.
I have factory reset my Lanturtle 3 times now, and the exact same behaviour is happening every time. It is filling up rootfs /dev/mtdblock3 and overlayfs:/overlay to 98%
/dev/root is at 100% all the time, even after factory reset.
/tmpfs is only at 2%
this behaviour is making my Lan turtle virtually useless as it does not even have space left for the credentials in the loot folder.