15 digits are a joke with regard to modern security recommendations
The 15-character limit is an existing limitation on BrickLink passwords and has
not changed. However, we will continue to increase security on our platform and
will communicate about any new security features as they become available.
It seems like you can use more than 15 characters using the "Reset password"
function, which in turn breaks BrickStore that only accepts 15 characters (users
were confused in the past, so I added the same character limitation in BrickStore)
This would also make it impossible to later change the password on BL's account
info page...