After digging around, this seems to be closely related to this post, for which there is a JIRA open with critical priority for over a year with no updates.
There is also multiple forums post discussing performance issues with GPT and SNAPPY. (Gpt performance, Performance of snap desktop and snappy, GPT batch processing abnormality, Graph Builder Editor bad performance, Multi-Threading and Performance of snappy / jpy, ProductIO.writeProduct() function takes longer to run when called in Python, Snappy running really slow)
Could we get some status update on this issue? That would be greatly appreciated.