Hello, So i'm completely new to Sony Vegas so i'm still learning. But one problem i have is that the video playback when scrolling through the video is so laggy its unbearable. As you can see in the video the preview quality is set to pretty low and so is the fps.
Here's the example video: 
My specs are: GeForce 980ti, i7 4790k, 16gb ram & i have sony vegas installed on a ssd.
Hopefully someone knows how to fix this because its really annoying :/ Cheers
Yes it is really bad / but check out the last posts of this thread:
What is your source footage container and codec?
It is probably your NV driver, but have you verified your GPU is interfacing at 16x pcie3.0 - GPU-z has a hover over for the interface.
Are doing any overclocking?
Have you verified you memory bandwidth is inline with what your dual channel speeds should be? "Winsat mem"
Have you pushed all windows updates and .net updates?
Are you running the last build of VP13?
The "..." after the frame counter is telling you Vegas is processing, and from what I could see it looks like its struggling to build the frame. Do you get the "..." when you try and move the timeline cursor back and forth on over the footage too?
Since you are working in 1920x1080x32 project settings, I would try converting a clip to Cineform-high.avi, HDCAM-SR-lite, or XDCAM-ex and seeing if your playback improves.
An AMD RX480 or Fury-x would be a better choice for Vegas work.