The minimum requirements for Windows 10 Mobile are lower than Windows Phone 8.1
The lowest-end phone would have 512MB of RAM and VGA camera
Microsoft has released official details about the minimum hardware requirements for Windows 10 Mobile platform. These requirements can give us a clear picture of what kind of low-end devices we may expect after the Windows 10 Mobile launch later this year.
The upcoming OS will be able to run on even lower hardware than Windows Phone 8.1, as Microsoft has relaxed even more the requirements. The very low-end smartphone running Windows 10 Mobile can theoretically have a screen resolution of 800 x 480 pixels, VGA camera, 4 Gigs of storage and 512 MB of RAM. Additionally, Microsoft has removed the requirements for having Bluetooth and an accelerometer, but low-res displays still need physical buttons for back, home and search. The company has also added support for Intel /x86/ processors, which would open the field to some interesting devices (phones and small tablets).
Microsoft is yet to reveal the very high-end possible specs supported by the platform, so we might wait until September / October before the upcoming flagship devices (the rumored Lumia 950 and Lumia 950 XL) become official.