Projects take a long time to open from Clarity PPM to Microsoft Project (MSP) with baselines in the Legacy driver. If the project has a baseline, the time to open the project almost doubles.
This is working as expected. Each baseline is a snapshot of the project plan, so the more baselines there are, the longer it takes to open/save the project. The amount of time it will increase per baseline is dependent on the size of the project including assignments, durations, number of tasks, etc.
Some options to help with improving performance: