The question is where the slowdown comes from. Once you know that you can figure out whether such a fix needs to come from the dreamhost side of the table or your own.
For what it’s worth, unless your shared server has specific issues it doesn’t appear to be server config creating a delay. I ran a simple php “hello world” page thru webpagetest.org. First byte was 0.392s, which seems to indicate dreamhost’s config is in order. If your page needs more server power there are two choices, optimize it for the server it’s running on, or pay for more power.