There are no specific compiler option(s), but You can switch to new Visual Studio compiler to compile the script (3rd party Inno Setup extension is needed: https://marketplace.visualstudio.com/items?itemName=unSignedsro.VisualInstaller) based on MSBuild.

Visual Studio in general is very well optimized, compiling, parsing etc. is really fast, which may reduce the times for you.

Also you may try switching the library, for example https://github.com/solodyagin/jsonconfig looks promising and is using different approach than koldev's JsonParser but its newer.