>>>It’s the effect of an old processor (1.5Gb)
I think you have got slightly mixed up.
1.5GB is the RAM memory your PC probably has.
That is nothing to do with the processor (CPU) though that is probably old as well.
However computer technology has moved on in the last 15 or so years since XP came out, and PCs then were not designed to handle huge amounts of video data throughput.
Data moves around a PC in something called the "BUS" and there is a "BUS" speed. The BUS speed has improved dramatically in 15 years (as had CPU speed, memory speed, graphics card speed and so on).
And all of these slower devices in old PCs just cant handle the huge volumes of data.
You did right to get a new PC (although not if you bought it from PC World - don't trust them).