Hi David,
The "cannot load from another platform" was a doc bug in 15.x; the wording pre-existed the cross-platform dump and load (XPDL) functionality but didn't get removed in error when XPDL was added.
It might still be worth trying the load with a regular uncompressed 12.5.3, but if that doesn't work than I'd try upgrading the dump to 12.5.4.
-bret