That slot is designed for a low-bandwidth WWAN adapter, so it won't have the ability to run the NVMe drive anywhere near what it is capable of -- and that's if it even works at all, since it's not a supported configuration. There also won't be any way to make the smaller drive a boot device.  Even if the drive does work, it'll be slow storage only -- not capable of much else.  
I find my laptop has two M.2 slots.  One is alongside the SATA connector, made for standard 22x80 M.2 NVMe SSDs. The other is an NVMe M.2 Slot for a 22x30 board.  I guess it can be called a PCIe m.2 slot.   I am using the standard slot with an M.2 SSD. I am exploring the idea of adding another M.2 SSD to the PCIe slot with a 2230 size board.  Is this doable?  Or do bios/motherboard configurations prevent such use cases?
latitude 5480 PCIe M2 2230, and M2 SSD