Hi @firat,
just an advice which does not directly solve your problem but maybe it helps. I have gotten this error once and switched to snappy for other reasons and the error was solved. I think the problem is not SNAP itself I guess, but honestly I have not figured it out after snappy was successful. hence you are interested in Displacement and PS look here to find some hints how to get snappy and the operators work.
About your last point I have some ideas:
The steps are TOPS Split → Apply Orbit File → Coregistration S1 BackGeocoding → TOPS Deburst
Instead of debursting each single image, you can deburst the whole stack, which is much faster. And you need the coregistration any way to build interferograms. To minimize data, because your RAM is limited to 8Gb, I recommend to select the bursts of interest and not all bursts of your subswath in the TOPS Split operator, this will decrease computing time significantly…but maybe you have done this already? An other guess, do your machine use a HDD? If that is the case I really recommend to switch to a SSD, in my case it was impossible to really work on a machine using a HDD, I encountered similar computing times and switched to a SSD, the problem was solved after that.
Hence you are looking forward to do PS analysis, I really recommend to switch to an Unix based OS as early as possible, you will find some help in the post I linked above.
I think these are just hints, if someone has a solution to the error message, that would be great!