Apart from the reduction in the data set as suggested above?
In case you also have many baselines in that project, you could try and set the Clarity > Admin > [Project Management] Settings > "Only Export Current Baselines When Opening Projects in a Scheduler" to TRUE.
A few other things come to mind
A PC with more RAM, better CPU, faster network connection to Clarity... same thing for the server....
What Clarity version are you on? And are you on Oracle or SQLServer?