Mainly because it's using MTP and not USB Mass Storage. But it should definitely not take 40 minutes to put a 1.5GB file onto your phone.
-- If you actually need to get in contact with me just tweet me rather than PMs its more efficient and I can get back to you faster.
Nexus 5 (D820)
: Purity | Franco Kernel
Nexus 4 (E960)
: Carbon | Franco r193
Older devices: Galaxy Nexus, ASUS TF101, Nexus S, Samsung Vibrant, G1