Being a theme, Jobroller search function is just based on the wordpress engine. There are a lot of factors that affects the speed of the query and that includes your server settings.
Wordpress is already being used by the biggies including CNN and so I believe it can scale up with your requirements given the ideal servers settings.
Please help our moderating team work more efficiently by not sending us support questions via PM. You can read more about how AppThemes support works
here. However, you can send a PM to follow up and remind me if I missed your support request/thread.
Thank you and have a nice day.
