A custom cartridge that seemed to be performing well in a sandbox has been installed...

To address the issue of increased page load times in a production environment after the installation of a custom cartridge, the developer should use the Code Profiler in the production instance and set the mode to Development Mode. This approach allows for real-time data collection from ongoing site traffic, which is crucial for identifying performance bottlenecks related to the new custom code. By setting the profiler to Development Mode and waiting a few minutes before refreshing the data, the developer can observe the impact of the custom code under actual traffic conditions. This method is preferred because it provides an immediate and realistic insight into how the custom code performs under normal operational loads, which is essential for effective troubleshooting and optimization in a production environment.