In order to know how quickly content is downloaded from your site you can use online-service host-tracker.com. But most likely the recieved values won't give you an exact answer to your question. To estimate how quickly content from your site is downloaded you must compare the results of content downloading from your site and the results of content downloading from any other site.
We suggest you to compare the downloading content speed from your and our servers.
So to get the results for comparison you need:
1With host-tracker's help to get the downloading speed of the test file (the size of the test file is 1Mb) from our servers and to save the results. These are results of the test that we have made already.
2To use any file from your server sized 1Mb (if you don't have such a file on your server, you can download our test file and upload it to your server).
3With host-tracker's help to get the downloading speed of the file from your server and to save the results. Now you need just to compare the recieved values.