sunny wagons came with a15 from factory in aus, under section 34 of the mods booklet for vic roads, you can use a replacement engine with bigger displacement if offered as an option on the model in question.

A12 sunny wagon and a15 sunny wagon were sold new in vic and aus, legal to put a15 into it! no effect to p plate laws at all

i almsot bought an a12 sunny to put an a15 into it. went through it all with vic roads, sedan needs engenieers, wagon doesnt as was sold new in aus with a15.... easiet upgrade for you, then a 32/36 onto it for a bit more oomph.