Never even heard of a 1.5. Even if it were possible, wouldn't they not believe you and just go by your block number for the engine size? Seems it would have to be torn down for them to be able to verify the size.
Oh, you mean the 1.5 IDI? I thought you meant there was a 1.5 TDI. I believe the bearings are different sizes on the crank, you would have to get cu$$tom con rods made as they would be way too short. I think you'd spend way more than you plan to save.
$$$ for sure for con rods if you want an engine that will actually start. With the 1.5 rods, the space above the piston would probably put your compression on the low end for even a gasser. You could probably have the crank built up and reground for the right bearing size, but again more $. Plus you didn't say what engine you have. I don't think it would work at all in an ALH block.