My question is, is this the normal definitive response rate for a no? Do 85% of agents really not respond at all (besides the auto reply 'got your query')?
There are no absolutes. On percentages responding or time responding. I actually once got a response to a query six months after the book had been published by a different agent/publisher. The two agents I know well will say they probably respond, other than a canned response no, to about .001% of the queries they receive. The vast majority of non-responses are because they get queries like "Hi, will you publish my novel?" or "I have written a 6,000 word book about the history of the world that will alter your beliefs!"
They also seem to get a ton of queries for stuff they don't rep. Amazing how many people are writing LGBT porn and sending it to agents who rep children and preteen books. But for every writer responsible enough to check the agent's credentials and look to see what genres they are looking for, there are a thousand who blast emails off to every agent listed anywhere for anything.
The magic of email the internet and electronic societies today is that stuff comes in greater volume and with a far wider range of quality. It's only natural that agents will simply ignore the drivel, hoping it just goes away. There's plenty more coming in tomorrow.
Advice? Six weeks is nothing, especially when agents are getting their kids out of the city on summer break. Be patient. And stop looking at response rates unless you're also reviewing your query's appropriateness and effectiveness. Send a dozen queries, wait a few weeks, send a dozen more. If you're like many writers, eventually you'll get a really good and encouraging response.
Jeff