Unfortunately, it is not possible to make the RTE any smaller than it is. We have broken down the installers for our various software packages as much as possible. For example, if you are creating an installer and select to install only the LabVIEW Run-Time Engine (ie. no other drivers like NI-DAQmx, NI-488.2, etc)
The download for the full LabVIEW 2017 run-time engine is 356.12 MB. There is a smaller version that is available for download but it also has limited functionality. It is intended for viewing Remote Front Panels in web pages. It does not contain the full run-time engine, but will allow some executables to run.
An application built in a specific version of LabVIEW must have the corresponding version of the RTE. Multiple versions of the RTE can be installed simultaneously, and all are freely distributed. Please see Drivers and Updates: LabVIEW Run-Time Engine
to find the correct run-time engine for your application.