My Sony Vegas videos are lagging. . . help?

So I make horse videos in sony vegas and i render them i hq . Everytime i preview (after i have rendered the video and i open up the video on my computer) the video it lags really bad and it's so horrible i can barely watch the video, and even iif i say screw it and try to upload the video it takes about 10 hours to upload to youtube which is really unsual for me.. Has anyone else had this problem or know how to fix it?