Still based on the Ubuntu 16.04 LTS (Xenial Xerus) operating system series, Ubuntu Touch OTA-18 is here as a maintenance update that plugs various annoyances and bugs to make the entire Ubuntu Touch mobile operating system more stable and reliable.
First of all, Ubuntu Touch OTA-18 introduces a new way for Ubuntu Touch to scale down and display wallpapers without affecting the performance of the system, which mostly benefits BQ Aquaris E4.5 users that use the default wallpaper, but it will also benefit devices with 1GB of RAM, yet the savings will vary depending screen and wallpaper resolutions.
Link to Article:
https://9to5linux.com/ubuntu-touch-ota-18-officially-released-with-performance-improvements-bug-fixes