Redmine

In Redmine, my page loads very slowly — for some accounts it takes about 10 seconds. The page only displays issues assigned to me and issues I’m following. There are about 200+ projects, and opening a single issue in a project takes about 1 second. How can I optimize the dashboard loading speed?Thank you very much for providing some suggestions.
Environment:
Redmine version 3.4.5.stable
Ruby version 2.3.3-p222 (2016-11-21) [i386-mingw32]
Rails version 4.2.8
Environment production
Database adapter Mysql2
Redmine plugins:
custom_field_sql 2.2
custom_users_as_assignees 0.0.3
redmine_agile 1.4.12
redmine_impersonate 1.0.0
redmine_issue_autoflow 2.7.3
redmine_issue_template 1.0.7
redmine_issues_tree 0.0.13
redmine_monitoring_controlling 0.1.1
redmine_my_page_paginations 1.0.2
redmine_searchable_selectbox 0.1.5
redmine_ueditor 0.3.4
redmine_work_time 0.3.4
redmine_workflow_hidden_fields 0.5.0
sidebar_hide 0.0.8
that_email_log 0.0.3
Because there are many plugins, we don’t plan to upgrade to the latest version.