a 1.5MB partition
That would be a Mint chocolate
I can guarantee that there are no partitions of that size and even 1.5 GB would be to small (it's probably a small piece of the disk that's a "leftover" you can't use)
If you used the entire disk for Mint, then the entire disk is used - right? But I have seen some oddities, so....
Simply resize the partition to make room for osx - I don't know if osx can do that - if not do it from the live CD, gparted can't change the active partition