These things are slow (by modern standards), yeah, but it was possible to get the model this far down ... how far can we go?
There was speech synethsis on the apple iie in like 64k of RAM and a 1mhz CPU.
Speech synthesis is far far far easier than parsing a human voice, especially when it doesn’t need to sound realistic (as was the case back then).
In the old papers about problem, there was vocabulary size of 64K words, because nothing was working for bigger vocabularies.
It is done using SVD and improves speed without sacrificing memory access patterns.