When generating a historypoint, the entire per-test coverage is loaded:
ie: collateSlicePairs .

This is rather expensive on very large projects, and is not used in the historypoint xml, nor the historyreport.

Consider not calling collateSlicePairs when generating a historypoint.

see attached thread dump:

Also look at the possibility for a non-source level only historypoint, if this is not already the case.