Back in late 2017 the game developers released a new patch for the Steam version of EAW (and only the Steam version) which fixed a few things (including re-adding multiplayer). One of the fixes rewrote the save function to prevent loss of data in larger and longer-lasting GCs - in particular the "save freeze" issue which has plagued a lot of mods in recent years, including ICW.
Unfortunately this means that saving now takes longer than it did previously, but with less chance of your save file getting corrupted. There is no way to speed it up (and in fact, the latest revision to the patch removed autosave after space/land battles in GC because users found that particularly frustrating/problematic).
More information direct from the devs:
Patch DetailsFollow-up Patches