It is X.Org Server 1.18.[1] Released in 9 November 2015.[2] The version 1.7 is from 2009. Trisquel 7 has the version 1.15.
[1] https://packages.ubuntu.com/search?suite=xenial&arch=any&searchon=names&keywords=xserver
[2] https://en.wikipedia.org/wiki/X.Org_Server#Releases
