Tune Apache2 for WHMCS

We're currently experiencing some large lag with our WHMCS site. We have a low traffic site but suffering massive lag and occasional loading issues.

We need someone to tune and refine our apache2 configurations to help with this issue, currently we're seeing an average CPU load of 79 with an available 2 CPU cores.

We're using a pre-fork version of apache, and would be up to any changes need to improve performance. We have done the standard evasive install with mod_timeoutreq.so Will need to checked on to make sure it was done correctly to prevent any slowloris attacks and DDoS.

Server version: Apache/2.4.18 (Ubuntu)
Server built: 2018-06-07T19:43:03
Server's Module Magic Number: 20120211:52
Server loaded: APR 1.5.2, APR-UTIL 1.5.4
Compiled using: APR 1.5.2, APR-UTIL 1.5.4
Architecture: 64-bit
Server MPM: prefork
threaded: no
forked: yes (variable process count)
Server compiled with....
-D APR_HAS_SENDFILE
-D APR_HAS_MMAP
-D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
-D APR_USE_SYSVSEM_SERIALIZE
-D APR_USE_PTHREAD_SERIALIZE
-D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
-D APR_HAS_OTHER_CHILD
-D AP_HAVE_RELIABLE_PIPED_LOGS
-D DYNAMIC_MODULE_LIMIT=256
-D HTTPD_ROOT="/etc/apache2"
-D SUEXEC_BIN="/usr/lib/apache2/suexec"
-D DEFAULT_PIDLOG="/var/run/apache2.pid"
-D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
-D DEFAULT_ERRORLOG="logs/error_log"
-D AP_TYPES_CONFIG_FILE="mime.types"
-D SERVER_CONFIG_FILE="apache2.conf"

Loaded Modules:
core_module (static)
so_module (static)
watchdog_module (static)
http_module (static)
log_config_module (static)
logio_module (static)
version_module (static)
unixd_module (static)
access_compat_module (shared)
alias_module (shared)
auth_basic_module (shared)
authn_core_module (shared)
authn_file_module (shared)
authz_core_module (shared)
authz_host_module (shared)
authz_user_module (shared)
autoindex_module (shared)
deflate_module (shared)
dir_module (shared)
env_module (shared)
evasive20_module (shared)
reqtimeout_module (shared)
filter_module (shared)
mime_module (shared)
mpm_prefork_module (shared)
negotiation_module (shared)
php7_module (shared)
rewrite_module (shared)
setenvif_module (shared)
ssl_module (shared)
status_module (shared)