So, @lylejk and @gubach, I'm happy to say there are new pre-release binaries/installers available for testing on the G'MIC web site : http://gmic.eu/files/prerelease/ (dated from today).
These new Windows binaries/installers have been compiled with
g++, version 6.2.0, so a quite recent one, and apparently this makes a huge difference
Particularly, the filter Deformations / Conformal maps now takes only a few seconds to run, in my VM Windows.
I'd be really interested by your tests with those new binaries.
Also, I'd like to thank SamJ (Sylvie Alexandre) for providing me with this new compiling environment !
And to be sure you are running the very latest version, check out the
ENSICAEN logo, it has been changed this morning.
Also @lyle, please note that there are a bunch of new DLLs that come along with the new binaries, so be sure you discard the old ones !