Finished in the end. Took 3 hours to complete.
How many masters / replica / data / rc ?
I have the same issue. upgrading vROPS 7.0 to 7.5 leaves my Master and Master Replica hanging on 4 of 9 run sql db upgrade. besides these two machines I also have two Remote Collectors.
The upgrade has been running for over 6 hours but it looks like the system is still updating, no screen hangs etc.