If Squad is anything like Project Reality then it's more complex than RO2. There are more mechanics you have to get to grips with, like the reviving. Weapon mechanics are also more complex than the fairly simple ones found in RO2. Artillery is also extremely detailed compared to RO2 and new players will no doubt find it intimidating.
That's just talking about the various systems, the playing style itself is way more demanding than RO2. Communication is more important and your role in the team is taken more seriously and with higher scrutiny.
I'd say it's mostly in the middle of Arma and RO. It tries to find a balance between realism and playability. More often than not it favours the Arma side.
I'm assuming Squad will have Project Reality-level mechanics when it is completely finished.