Since the connection is so very slow, caching DNS queries locally is going to be extremely beneficial. Why? Because you don't want a DNS query to fail because your bandwidth is saturated. This is a very common case while a web browser is downloading from multiple servers at the same time. This is common with displaying web pages from large sites because they put images on one server and html content on another.
I like using djb's dnscache, as it's simple and does just one thing. It does come with a whole bunch of baggage that you may not care for, but it works for me and is easy to set up and tear down and throw away.