It is a bit like calling someone on the phone and asking why your car is running slow. There are just too many things to check and it is hard to diagnose without being able to put our hands on the system.
However, here are some things to check:
1. Are there any error messages or exceptions? The catalina.out log entries might be trying to tell you something is wrong.
2. Is search working? If SOLR is broken, the repository will continue to function but it will be very slow. Can you add content and, after a few minutes, search for it using a full-text query? If not, check the logs for search-related errors.
3. Are your server resources max'd out? Check that you have enough CPU and memory. Related to memory, is your memory swapping? Swapping kills performance.
4. Related to the previous, are you running the database on the same server as Alfresco? Moving the database to its own server can be helpful in speeding up a sluggish server.
5. Are you running SOLR on the same server as Alfresco? Again, why not free up some resources by moving SOLR, which is very resource-intensive, to its own machine.
6. Do you have enough database connections configured?
7. Speaking of database, maybe you have some slow queries and need some indices to be created. Have a DBA take a look.
8. How fast are your disks? You should be running SSD's, if possible. If that's not possible, run on the fastest disks you can.
9. What customizations and add-ons have you installed? Maybe they are not performing well.
10. Is there a lot of network latency between you and your server?
Those are the first ten things that come to mind.
Ultimately, Alfresco is just another Java-based web application. You should be able to find plenty of resources online related to tuning Java-based web applications.
