The standby instrument is very comprehensive and written in XML. The current XML renderer in MSFS is GDI+ which is not very efficient when rendering such complex pieces.
There is the option of NanoVG in Devmode which is what Xbox uses and which will replace GDI+. That has a very small FPS footprint and is slated to replace GDI+ for XML gauges.
Until that time comes, the only other alternative is to do the instrument with JavaScript which will take months.