On my system right now, I have 24 apache workers, each with a nominal RSS size of ~100MB. If you just add them all together, you'd conclude that I have 2.4 GB of apache processes + 250MB of mySQL on a 1GB Linode, Oh NOES!! But here is the thing, 'free' reports that I've got 50MB free, 14MB of buffers, and 276MB of disk cache, and I'm only using 40MB of swap. That doesn't add up.

The thing is, the RSS size of apache workers with mod_php generally includes a lot of shared memory. Using a script that tries to estimate the actual memory size of multi-process daemons suggests that apache is using something closer to 390MB, with 100MB of that shared, and about 290MB distributed amongst the individual processes, which only works out to about 12MB of dedicated memory per worker.

So, bottom line, your problem probably isn't apache at all (at least not from the evidence you've shared). The nginx reverse proxy is still worthwhile to do, eventually.