Huge time before HTTP server responds disconnects premature

My application performs a HTTP request to a front-end of HA-proxy. The back-end forwards this to a server that accepts my request, but then starts a local proseccing for over 150 seconds before it starts transmitting data.
My configuration looks as follows:

global
    pidfile     /var/run/haproxy.pid
    maxconn     100
    daemon

defaults
    timeout connect 5s
    timeout client 120s
    timeout server 120s

frontend scada_104
    mode tcp
    bind *:2404
    acl ifs_1 src {{ ifs_1 }}
    use_backend 104_backend_ifs1 if ifs_1
    acl ifs_2 src {{ ifs_2 }}
    use_backend 104_backend_ifs2 if ifs_2

backend 104_backend_ifs1
    mode tcp
    server vccu-104-ifs1 192.168.56.10:2404 verify none

backend 104_backend_ifs2
    mode tcp
    server vccu-104-ifs2 192.168.56.10:2405 verify none

frontend sam_vvpn_rest
    mode http
    bind *:1443 ssl crt /etc/ssl/certs/sas2.pem
    use_backend sam_backend_vvpn

backend sam_backend_vvpn
   mode http
   server vccu-sam-rest 192.168.56.10:80 verify none

frontend sam_ccu_rest
    mode http
    bind *:443 ssl crt /etc/ssl/certs/sas2.pem
    use_backend sam_backend_ccu

backend sam_backend_ccu
   mode http
   server ccu-sam-rest 192.168.56.10:81 verify none

The font-end used is sam_ccu_rest.
Is there a certain keep-alive system that I should use here or configure here?

Hi,
You may want to look at that section:

defaults
timeout connect 5s
timeout client 120s
timeout server 120s