Fair enough, I don't really use Zooms for much. I bought the 55-200 first after getting the camera but it's turned out that 1) most of my pictures are events or street style, and 2) I am enjoying primes a lot more. So my 15-45 & 55-200 I rarely even have with me. I most commonly take out the Sigma 16mm and the Canon 32mm (or the EF 50 f/1.4 with Viltrox speedbooster) when I'm out. If I were doing nature photography I'd probably use zooms more though.
How is the 18-150? I've wondered for a while if that would be a way to simplify the 15-45/55-200 into a single lens.
I bought the M5 a few years back, and love it. It's notably more compact than any of my DSLRs. With the 15-45mm or 22mm prime, I can slip it in a very small pocket or part of a bag.
Having said that, I also do have the 18-150mm and it's a great lens. Optically better than any of Canon EF-S 18-135mm lenses (there are 3 of them). But yes, it makes the whole package a bit longer than the shorter lenses obviously.
However, for a single lens option with some reach, it works really well. And yes, I find it covers 90% of the shots that a 15-45mm and 55-200mm will do. (The extra 50mm between 150mm and 200mm is not that noticable.. and 24MP or 32MP images crop quite well).
I also have the Rokinon (Samyang) EF-M 12mm f/2 lens, and I use that for astro photography or as an UWA option too (it's a really good lens and amazingly compact for what it is) So at times I go out with those 2 lenses, the 12mm f/2 and 18-150mm. But for a 1 lens option, I go with the 18-150mm most often, or the 15-45mm when I need a truly compact zoom. Interestingly, my copy of the 15-45mm is very sharp.. I think some early adopters got poor copies, but I have owned 2 and both were very good in terms of resolution, colour rendition, etc).
Regarding the original theme of this post, I am very much looking forward to Canon putting IBIS in a future EF-M camera... it would breath even more life into my Rokinon 12mm f/2 as well as my Canon 22mm f/2 prime (another great lens).
Cheers
PJ