TLDR - Begining with Grav 1.5.10 and Grav 1.6.0, the Deferred Twig extension is available and an update to your theme is strongly recommended to ensure you won't have issues with plugins going forward.
What started as a Grav 1.6 only feature, has been back-ported in to Grav 1.5.10, as it'...
Most people that are initially developing with Grav either modify the default Antimatter theme directly, or copy-and-rename it, providing a separate theme to modify. Each of these approaches have their own issues.
By modifying the base theme directly, any theme update will potentially overwrite changes made. By copying the theme, the theme will not be overridden, but updates and fixes to the core theme, have to be manually merged over to the copied theme.
There is a much simpler, and much more maintainable method however: Theme Inheritance.