Limiting parameters on custom query?

Specifically for a MailChimp query, I'm pulling in my member data from a few of my lists using this:

let
Source = MailChimp.Instance("lists/{list_id}/members?count=15000"),
lists = Source{[Key="lists"]}[Data]

in
Source

3 of the lists are relatively small so I don't have any problems, but one of the lists is rather large and keeps timing out. I'm trying to reduce the number of parameters that the query is calling from the beginning so that, hopefully, it can reduce the amount of data coming through and stop timing out. I have 33 different parameters that it's loading when I really only need 5 or 6 of them.

Here's the documentation on the API:

http://developer.mailchimp.com/documentation/mailchimp/reference/lists/members/

Thanks!

(FYI: the 15000 count at the end of the URL is to bypass the default limit of 10 responses. Using a smaller count will cut my data off)