Original Motorola DROID Turbo receives a security update from Verizon
The update brings the latest Android security software to the DROID Turbo and it also adds improvements to call performance. Just because this is the OG Turbo doesn't make it totally irrelevant. Verizon still offers the device as a mid-range handset priced at $480.
Verizon suggests that after receiving the notification that your Turbo has received the update, you make sure that the phone is connected to a Wi-Fi network or a strong Verizon cellular signal before starting the updating process. Also, your battery should be fully charged before you start the update.
On Motorola's support page, it says that the Motorola DROID Turbo is still slated to receive Android 6.0 "pending partner support." Which means that if you still own this phone, you need to keep pushing Verizon to support an update to Android 6.0.
source: Verizon, Motorola via AndroidCentral