I think all cars' AC units run better when at speed (better air flow to cool engine and more power going to electronics). I don't think its a 2.5 vs 2.0 thing. It's more of the strictly manual knob ac found in lower trims being cooler than the electronically controlled AC units found in higher trim Mazdas.
My thinking was that the 2.5 may have more torque at idle to turn the compressor, so it may cool a little better. Not sure though. At speed it's fine.
It's also possible her a/c is a little undercharged even though its new...will investigate more.