Why does my PS2 emulator run at 20% speed?

Emulator PCSX2. It runs in 100% 60FPS when started, I run the game, in the settings, start a new game, create savings, then it goes the first cut scene video - everything in 60FPS alright... As soon as the real gameplay started, it drops to 30-20% and 13 FPS so impossible to play. What can cause this problem? I set everything as in Youtube tutorials and tried to run more or less a simple and small game as Ben 10 which was 600 Mb.

2021-02-27T02:39:47Z

It always goes with this message "GSDX out of memory"... What does it mean? 

2017-04-11T00:37:33.809Z