I have install the WP Fast Cache plugin on the server. I also removed Askimet, as no one has commented here, and a registration plugin. These plugins can cause slower performance and frankly the one was not working as advertised anyway. You should be seeing faster page serves now.
If you click on a picture to see a larger view then this will still take some time. The larger photos are not cached and have to be retrieved from the WordPress/MySQL Database.
I also install a 512MB USB stick into the other RasPi onboard port. I then edited fstab and set it as a swap file. I changed swapiness to 40 and increased cache size to 512MB from 100MB.