It uses to take almost 4 hours to generate and nowadays a bit less than 2 hours which is still a lot. Build time trend:
The huge drop from 220 minutes to 100 minutes is git lg 3d7e37edd08edd4504bff920cc0b0972917f5795..4a975b8099ee11b15421d03be02206935a8422f1 which contains the refactoring of parser tests. Potentially parser tests are no longer participating in the coverage.
Presumably the parser tests are no more running for the coverage job. Might not be a big deal.