speed improvement is a very tricky task so here is a common issue which makes the server slow but there could be other reasons too :)​

Configuration:

1) Monitor server resource and make sure it does not consume 100% all the time otherwise you need to upgrade hardware configuration (mostly hosting provider provide tools to monitor hardware usage) 
2) configure/start odoo with worker 
3) proper configure Nginx web server so it could handle the log-polling request 
4) configure Postgres server according to your resources using pgture

Profiling:

5) profile odoo server using flame graph which provides an overview of which method take most of the time
6) using odoo build profile pinpoint the method line which takes much time and try to resolve it using code optimization
7) monitor progress using pgboucer and make a report which provides which queries take most of the time. here you can find where most of the time odoo waiting for Postgres response

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