For the DRC taking more time: The drc is getting more and more features and checks added with each version, so a slight increase in calculation time could be expected. But from one minute to 10 minutes seems like a regression.
To investigate this the complete project is needed, preferable with a v7 and a v8 version (so the increase in drc calculation time can be reproduced).
You could open a gitlab issue with the “confidential” checkbox set - so the design files are only available for the core developers.
Without the archived projects there is not much that can be done.
In order to investigate, specific designs need to be shared with the development team. They can be shared confidentially if needed.
The options for reporting performance problems that will lead to them getting fixed are:
Report as an issue on GitLab, marking as confidential if needed, with the design attached. Follow the instructions at Report an Issue | KiCad EDA
Get paid support from https://www.kipro-pcb.com/ - they take problem reports such as performance issues privately, and can do things like sign NDAs where required.
Performance issues can depend heavily on a specific design.