On top of the performance hints Juraj provided, have you debugged your site in Visual Studio? Is it possible you have some bad code? You might want to also look into cleaning up your database data. A database 87GB in size probably has a lot of junk in it that is very old or not used. So take a look at:
- event log settings, make sure they aren't set over say 10k records
- analytics, make sure you perform cleanup of the data on a regular basis. Should have no more than 12-18 months if you're using any of the EMS features.
- contacts, split them off into another database, this helps with performance and keeping your CRM data seperate
- activity tracking, make sure to clean up your contact's and their activities on a regular basis.