One reason that the Bluetooth drivers from Intel may not have installed properly is that you have an OEM version of Windows 7 installed (pre-installed by Dell, just as other manufacturers do). Sometimes OEM versions include modified drivers (by the OEM - Dell).
Try the Bluetooth drivers for your Inspiron 15R 5520 from Dell Support -
Drivers & Downloads | Dell US
Under "Network", there is one called "Intel Centrino Wireless-N 2230 Bluetooth Application" -- try that one. Your Intel Centrino wifi appears to be working fine.
Be sure to create a system restore point 1st -
START | type create
| "create a restore point"
All device drivers for x64 must be signed. Just curious - how do you know the BT driver from Intel is unsigned?
Happy New Year!