vegas is bad at this kind of thing, even computers that can absolutely handle it in theory (ryzen 3950x/rtx3090 still chugs when i have a moderate number of things happening at once). i've been using vegas professionally since the middle of last year, and i've lost hundreds of dollars in productivity cause it just blows (it's a side hustle tho so i cant be bothered to learn anything else)
here's what's made it marginally better for me:
- shift-b to prerender sections with transitions/effects
- changing the quality to "Draft (auto)"
- make sure you have hardware acceleration on and your most recent gpu drivers
- if you're on vegas pro, turn off "smart resample"
- accept that it's gonna be bad, take a deep breath, and use your imagination