Progress bar not synced with upload

I have a form with a drop-zone file element. I created a progress bar via the tutorial and it works except it goes too fast. It is set to upload percent with the +’%’ added. but when uploading 2 - 5mb files the progress bar goes across in about 15 seconds and the images take about 1.5 minutes to upload. I tried a spinner on the button set to upload and it does the same thing. It ends before the upload is complete. Any ideas? I’ve tried all I can think of with no luck. Thanks!