Trainers in the overworld will have 10 IVs in all stats and 0 EVs in all difficulties. Boss battles may have ideal EVs/IVs depending on what difficulty you’re playing on. Normal difficulty starts to see Pokemon with non-neutral natures, 31 IVs, and beneficial EVs starting at Gym 6. On Hard difficulty that starts at Gym 4.
I’m not 100% sure about Memory Chamber but considering how EVs are assigned in Insurgence I feel like they wouldn’t have ideal EVs. IVs may all be set to 31 though since that’s easy to do.