So find a friend who has it and try it out on their machine?
That way, when you find how shit it is, you haven't needlessly thrown money at Microsoft, nor committed to an OS that is worse but you can't be bothered with the effort of uninstalling and reinstalling.
> And why, in 2.2 years, does a computer become so slow?
It doesn't? I'm pretty sure (ignoring faults) the hardware will be running at the same speed it always was.
The problem will mostly be shitty software making stuff take longer, with maybe a sprinkling of genuine delays due to having to look at more data.