I'm getting close to being through with the first half of MO, but this has gotten really tiresome. The vast majority of the time, whenever I go to save or load a game, it takes 10-15 seconds or more. Given how I've been playing mental the entire time, this really adds up. It's been so long since I played RA2 I kind of assumed this was nothing abnormal, or was alteast related to how long it took for Ares to get implemented, but on occasion, it's taken absolutely no time for the save and load screens to load. Actually saving or loading a game doesn't take long- just the act of getting to the save and load options takes an inordinate amount of time that really, really adds up.
Is this just how the mod is right now or is this a bug?
Do you have multiple DVD drives or a virtual DVD drive running? I'm not sure if that was the cause, but I remember I used to have that exact issue with base RA2 or YR where opening the save or load menu would take forever, back when I had a computer with multiple disc drives. It's quite possible the issue remains in Mental Omega.
I think it also only happened after I already had a few save files, though I can't remember for sure. Try out base RA2 and YR and make a few saves, then see if the same happens there.