Hi @Chozinentropy,
I can tell you from experience that 16Gig is not enough (without adjusting the read-per-batch parameter) when working with the Silva database as this is essentialy writing the entire database into memory.
The error you are seeing MAY be related still to the insufficient memory issue, though this was fixed after qiime2-2019.7. What QIIME 2 version are you using?
A couple of others things to check: make sure the file-paths are correct, or that you are running those commands in the same directory as the classifier and rep-seqs file.
Lastly, can you try running your training the classifier with the Greengenes database which we know will not have these memory issues and if it works we can work out the issues with Silva.
But so far, everything to me still points towards insufficient memory isues.