The slingshot 250 will definitely accommodate your EM 5 with a 12-40 attached. There is also ample space in the camera padded section for the 40-150 lens.
I use it with a Nikon D500 w/ both a battery grip and an 18-300 lens attached. I chose to put my tripod accessories, video mic, and extra batteries in the lower section for quick access. I put two other lenses in the top section. The top section is spacious, although no padded dividers, so I put my lenses in their individual lens bags to keep them protected.