With my ThinkPad T450s running Mint 17.1, I have found that Bluetooth is always turned on by default when booted, regardless of whatever changes I make to the Bluetooth adapted in the System Settings panel.
Bluetooth can be disabled by default on startup by adding the following line to the
# Disable bluetooth on start up. rfkill block bluetooth
This must be added above the
exit 0 line at the end of the file.