Long delay when restarting haproxy servcie

Hello HAProxy people,

When restarting haproxy a considerable delay is observed and the following is printed in the log:
Jan 30 15:05:02 dev-api-proxy haproxy-systemd-wrapper[9576]: haproxy-systemd-wrapper: SIGINT -> 9595
Jan 30 15:05:02 dev-api-proxy haproxy-systemd-wrapper[9576]: haproxy-systemd-wrapper: exit, haproxy RC=0
Jan 30 15:05:38 dev-api-proxy haproxy-systemd-wrapper[9688]: haproxy-systemd-wrapper: executing /usr/sbin/haproxy -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -Ds

Where could shall I look for the root cause of this delay?
The server isn’t used for anything else and is not really doing anything, so it is not likely to be caused by a resource bottleneck.

Haproxy version 1.6 on Ubuntu 16.04.

Thank you in advance,