I've never seen such issue here.
What version of Opera and Windows are you using? Do you use any antivirus, security suite, antimalware or any other program that keeps monitoring your computer activities?
What about extensions?
Anything changes if you disable hardware acceleration?
For those facing the 'out of memory' issue:
What is your OS?
What is your graphics card?
Any program running in background, like anti-virus, security suite, anti-malware, etc?
I'm using Opera 42.0.2393.94
Windows version 8.1 64 bit
Graphics Card NVIDIA GeForce GTX 980 Ti
If I run Opera with the VPN it uses up memory and crashes. If I run it without the VPN it works fine.
Running Youtube and streaming video causes the memory leak to crash the browser much more quickly.
It is reproducible every time and using the Task Manager you can actually watch the memory usage ramp up till it crashes.