Yeah, I was going to suggest deleting the sound files, but it looks
like I already suggested it ;)

There are 16mb sticks btw, which is why the memory stick storage space
isn't commonly an issue. The 16mb sticks came out fairly early on,
and continued to be used with the ERS-7 models, so are/were pretty
widespread. You may be able to find one on e-bay if you are so
inclined, or "convert" another memory stick to become a "pink memory
stick". (although I don't have any first hand experience with the
latter)

As an alternative to doing without sound, you can also convert the wav
files to 8bit/8Hz to save space. (then also change ms/config/
tekkotsu.xml's sound.sample_bits and sample_rate settings to match)

-ethan