i also own the 15-45 and the 18-55...what i don't like most about the 15-45 is the collapsible design. i feel i'm missing moments having to extend the lens and i don't trust it (and me) to leave it open all the time. what i don't like about the 18-55 is that it starts at 18
i have the ef-s 15-85 as well which solves both complaints but it is a beast on the M5 with the adapter
i also dipped my toes into the fuji system and their 16-50 kit lens is really good...and they have the mirrorless equivalent of the ef-s 15-85 i've been asking for from canon: 16-80 f4, which i'm more and more tempted to buy...