Julia 1.8.2 message ERROR: LoadError: too many parameters for type

[sgaure]

You should use a static vector for this purpose. A Vector will only place a pointer in the julia struct, whereas the vector itself will be on the heap. Either an SVector or an MVector:

using StaticArrays
struct ...
   path::Cint
   ...
   projparam::SVector{15, Cdouble}
   ...
end