“Java heap space” indicates insufficient memory.
The S1 TOPS Coregistration is a chain of multiple separate operators. RAM is often not sufficient to execute all steps in sequence, especially when you select many bursts in the Split operator.
I recommend to execute the steps separately, especially reduce the number of bursts as much as possible and make sure that you only use VV polarization.
Please have a look at this tutorial: DEM generation with Sentinel-1 - Workflow and challenges