I managed to change it. But when I go back into the registry again, it went back to 256
I have Lumia 830
I also have a Lumia 830, I managed to do it, it now shows Virtual Memory - 1,00 GB.
I downloaded the latest Interop tools (1.9.437.0) from
XDA (there's a download link a bit further down), You need to download both the InteropTools and Dependencies (presumably for ARM), and install the dependencies before you install the tools. Once done, it should show up in the app list. Open it and before changing anything, in the burger menu tap on Unlock > Interop unlock and there turn on "Restore NDTKSvc" if it wasn't already. Restart inbetween, I guess (not sure if entirely necesary, but that's what I did). After that change the registry entry and restart.
I first tried this with some older version of Interop Tools (I got the link from some Windows central article), that one, once installed, was only accessible through settings > Extras. I could browse the registry and change something, but the changes didn't stick.
If you had this one, maybe that's why it didn't work, if you have the latest one, check that Unlock thing