Calling the sub vi's continuously inside loop makes sub vi over head. This causes delay in execution speed. To over come this issue we can make the sub vi as inline vi ( Refer following articles and discussion forum for more details).
In one of our project we set both inline & subroutine VI properties (wherever possible) to increase the execution speed of sub vi.
https://www.ni.com/docs/en-US/bundle/labview/page/vi-execution-speed.html
https://forums.ni.com/t5/LabVIEW/Inline-subvi/td-p/1279078
