Hi Martinverbic, 
Here are a couple tricks I use to maximize my memory on digital ocean. I recently shared theses tips plus more in a medium article. I was trying to host multiple ghost blogs on one droplet so these tweaks were important.
Optimizing your Digital Ocean Droplet
Swap File
Swap is a space on a disk that is used when the amount of physical RAM memory is full. When our droplet runs out of RAM, inactive pages are moved from the RAM to the swap space. The swap file will not be as fast as ram, but it will definitely help.
Note: If you have 1GB of RAM, then it is recommended that your swap file be 2GB.
Log Rotation
The Ghost blog platform doesn’t automatically set up log rotation when it is installed. As a result, Ghost will perpetually append to its log files until you run out of disk space. Setting up log rotation will ensure you only keep one week’s worth of ghost logs.
Use Cloud Flare
Adding the free version of Cloudflare will improve performance by blocking bad actors as well as caching your site on their CDN, which decreases the load on your server.
Reduce Ram Usage by MySQL
This tip dropped my RAM usage by 16%
I hope these are helpful,
Jaz