Poor application performance behind nginx reverse proxy

I started noticing very slow page loads on my Jira server. I figured out that this only happens when Jira is accessed through nginx, but if I use SSH port forwarding to the server and access the backend ports directly, page loads are instantaneous.

nginx config (/etc/nginx/sites-enabled/support.example.org.conf):

## Jira
##
## Modified from nginx http version
## Modified from https://confluence.atlassian.com/jirakb/integrating-jira-with-nginx-426115340.html
## Modified from https://raymii.org/s/tutorials/Strong_SSL_Security_On_nginx.html
##

server {
  listen 192.168.118.32:443 ssl;
  server_name support.example.org;
  server_tokens off;

  ## Strong SSL Security
  ## https://raymii.org/s/tutorials/Strong_SSL_Security_On_nginx.html & https://cipherli.st/
  ssl on;
  ssl_certificate     /etc/letsencrypt/live/support.example.org/fullchain.pem;
  ssl_certificate_key /etc/letsencrypt/live/support.example.org/privkey.pem;

  ssl_protocols TLSv1.2;
  ssl_ciphers 'ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256';
  ssl_prefer_server_ciphers on;
  ssl_session_cache shared:SSL:10m;
  ssl_session_tickets off;
  ssl_session_timeout 1d;


  access_log  /var/log/nginx/support_access.log;
  error_log   /var/log/nginx/support_error.log;

  location /jira {
    gzip off;

    proxy_read_timeout      300;
    proxy_connect_timeout   300;
    # proxy_redirect          off;
    proxy_request_buffering off;
    proxy_buffering         off;

    proxy_set_header    X-Forwarded-Host    $host;
    proxy_set_header    X-Real-IP           $remote_addr;
    proxy_set_header    X-Forwarded-Ssl     on;
    proxy_set_header    X-Forwarded-For     $proxy_add_x_forwarded_for;
    proxy_set_header    X-Forwarded-Proto   $scheme;
    proxy_pass http://localhost:8081/jira;

    client_max_body_size 2G;
  }


  include snippets/letsencrypt.conf;
}

Some of the proxy settings are things I tried already and they ranged from minor improvements to no improvements, but the performance is still abysmal.

Jira config: (/opt/atlassian/jira/conf/server.xml)

<?xml version="1.0" encoding="utf-8"?>
<Server port="8005" shutdown="SHUTDOWN">
    <Listener className="org.apache.catalina.startup.VersionLoggerListener"/>
    <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on"/>
    <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener"/>
    <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener"/>
    <Listener className="org.apache.catalina.core.ThreadLocalLeakPreventionListener"/>

    <Service name="Catalina">
        <!--
         ==============================================================================================================
         HTTPS - Proxying Jira via Apache or Nginx over HTTPS

         If you're proxying traffic to Jira over HTTPS, uncomment the below connector and comment out the others.
         Ensure the proxyName and proxyPort are updated with the appropriate information if necessary as per the docs.

         See the following for more information:

            Apache - https://confluence.atlassian.com/x/PTT3MQ
            nginx  - https://confluence.atlassian.com/x/DAFmGQ
         ==============================================================================================================
        -->

        <Connector port="8081" relaxedPathChars="[]|" relaxedQueryChars="[]|{}^&#x5c;&#x60;&quot;&lt;&gt;"
                   maxThreads="150" minSpareThreads="25" connectionTimeout="20000" enableLookups="false"
                   maxHttpHeaderSize="8192" protocol="HTTP/1.1" useBodyEncodingForURI="true" redirectPort="8443"
                   acceptCount="100" disableUploadTimeout="true" bindOnInit="false" secure="true" scheme="https"
                   proxyName="support.example.org" proxyPort="443"/>

        <Engine name="Catalina" defaultHost="localhost">
            <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true">

                <Context path="/jira" docBase="${catalina.home}/atlassian-jira" reloadable="false" useHttpOnly="true">
                    <Resource name="UserTransaction" auth="Container" type="javax.transaction.UserTransaction"
                              factory="org.objectweb.jotm.UserTransactionFactory" jotm.timeout="60"/>
                    <Manager pathname=""/>
                    <JarScanner scanManifest="false"/>
                    <Valve className="org.apache.catalina.valves.StuckThreadDetectionValve" threshold="120" />
                </Context>

            </Host>
            <Valve className="org.apache.catalina.valves.AccessLogValve"
                   pattern="%a %{jira.request.id}r %{jira.request.username}r %t &quot;%m %U%q %H&quot; %s %b %D &quot;%{Referer}i&quot; &quot;%{User-Agent}i&quot; &quot;%{jira.request.assession.id}r&quot;"/>
        </Engine>
    </Service>
</Server>

When I test directly, I enable the default connector:

<Connector port="8080" relaxedPathChars="[]|" relaxedQueryChars="[]|{}^&#x5c;&#x60;&quot;&lt;&gt;"
                   maxThreads="150" minSpareThreads="25" connectionTimeout="20000" enableLookups="false"
                   maxHttpHeaderSize="8192" protocol="HTTP/1.1" useBodyEncodingForURI="true" redirectPort="8443"
                   acceptCount="100" disableUploadTimeout="true" bindOnInit="false"/>

What am I doing wrong or how can I improve the performance?