Dear User,
The proper method to merge 2 Sentinel-2 images is the mosaic. In SNAP 2 mosaicking methods are present: 1) ‘Multi-size mosaic’ module where the resampling is not needed; 2) ‘Mosaic’ that requires a resampling as pre-processing step.
I guess that your error is due to your laptop, could you please specify OS, RAM and available space on your disk? Another point is related to the output format, in fact I would suggest to use the default one BEAM-DIMAP.
Please do not hesitate to contact us for any further clarification.
Best Regards,
Fabrizio