with the commnad apache2 -v you can find out you apache version. If its higher than 2.4.18 first do 

a2enmod http2

then

# for a https server
Protocols h2 http/1.1


# for a http server
Protocols h2c http/1.1

that will speed up your load time about 60 to 70 percent. (depending on file size and equipment performance)

if you have a lower version you can build apache from source

if you are using php upgrading to php 7.0 will give you twice the performance with half the power consomption. if you can't apt-get install php 7.0 you can build it from source