I have a similar problem - I'm importing a 2-hour video, cutting it down to 1 hour, and the result is a file 6x larger than the original. I finally got that to render, but I cannot get it to upload to youtube. It's not the first time I've edited a video to be shorter and ended up with a larger file. I don't understand that.
I ended up using theWindows 10 Photos app. It took me less than half the time to cut the parts I didn't want and I had no issue exporting and then uploading to youtube. And, the final file size was just under the original. I'm done with Rush.