Low speed when loading.

Difficult to investigate with so little information.

First, whan you say "access to activities" do you mean get the list or get the detail of one activity ?

I can confirm this is not normal.
For instance you can test perfs.projeqtor.org, with about 10000 activities.
Listing all activities is less than 3 seconds.
Getting detail for 1 activity is abot 1 second.

Check log file for errors of too verbuous logging.
You can possibly check log files for mysql and activite the "long query logging" to check which queries are long.
Check your CPU, and HDD accees.
Maybe it's just configuration of mysql allowing too small cache...
It's difficult to help more without investigating on the machine.