Jodi,
There are many reasons for a Moodle site to be slow, and some of those are related to the system setup and configuration - the responsiblity of your IT dept.
However if your course, in particular, is slow then I would start looking at your course. The large size of your course leads me to believe you might have a lot of pictures or graphics loaded into your course, or perhaps a lot of large documents - PDFs, PowerPoints, etc.
The first thing I look for is resized pictures or graphics. Many instructors upload large, high resolution pictures, then set the size to something very small (e.g. 1" x 2", or 100px x 200px). This really slows down your course for two reasons 1) it takes time to transmit the large picture file from the server to the browser, and 2) then the local computer has to resize the picture as it is displayed. You can notice this if pictures in your course display very slowly. The solution to this problem is to resize and compress your pictures _before_ loading them into your Moodle course.
A second problem I've seen (especially in Moodle 1.9) is courses slowing down when a page contains a lot of text copied/pasted from Microsoft Word. MS Word puts a lot (and I mean a lot) of useless hidden code in documents that gets copied over when you copy/paste text into Moodle. If you have done this, open the Moodle document edit window and click the HTML < > icon. You might see several pages of code. If that is the case, use the editor's W (clean MS Word) icon to see if it can remove most of the code. If not, you will want to delete the text in Moodle, then save your MS Word document in plain text format before doing a copy/paste. Reformat the text in Moodle with the Moodle editor.
If you have a lot of large PowerPoint files (especially with a lot of graphics), those can make your course appear slow when students access the ppt file. The solution is to save the ppt file with compressed graphics.
Large PDF files can also load very slowly and make your course appear slow. Adobe Acrobat PRO can save PDFs in a compressed format. Another option is to break the PDF file into several sub-files or pages and place them in a Moodle Book.
I also advise instructors to clean out unused files from the Moodle 1.9 files area.
I hope this gives you a start. I'm willing to take a quick look at your course if you want to give me access (reply privately if you do this).
-Floyd