You only have 1GByte RAM on your S2.In reality you even have less. Your video gpu takes memory away too. You need a device with at least 3 gigabyte on HD 1920x1080 and 2 gigabyte on HD 720p screen resolution devices.

I have a 1 GB RAM 540x960 resolution device, I think Opera 12 (Classic) handled more than 10 pages without having to reload them. So, this is not a valid excuse, the new Opera can be improved.