I believe with the GPU Acceleration option on your Vegas Pro 18, you can certainly use that in order to speed up the rendering process for your large video.
The steps to do it are the following: Go to the Options Menu in Vegas, then go to Preferences and then click the Video tab, then click the drop down where it says GPU Acceleration, if you have a compatible graphics card on your PC, it should appear on the menu. Then click OK.
Here is a video I found to help you on that: https://www.youtube.com/watch?v=l3qLvN0CN_w It may say Vegas 17 but it should be the same process for Vegas 18 as well. 🙂 Good luck!
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