Unfortunately I do not have my OG Play. My current Play+ is an upgrade of the old one that I had sent back 
I also suspect that processing is the bottleneck, that’s the hypothesis I presented in Load sample packs faster on the Play - Wishlist / Archive - Polyend Backstage:
However, if this hypothesis is true, could a case be made that this conversion needs to happen only once? The device (or the users) could pre-process the WAV files into this internal format and write the new files to the SD card (or larger card), which would then act as a cache.
In other words, if all that time is spent creating a new intermediate form that is easier for the Play to work with internally, let’s work on a way for us users to leave that intermediate form on the card, so it’s not done again. Space is “cheap”, that 128 MB microSD card was less than $19. Right now the time it takes me to load sample packs is pretty much why I don’t use the device as much as other devices that load my patches nearly instantaneously. @Mitch, what do you think?
Then again, it could also just be the internal card reader, but 1 MB/s is really slow.