I would think that the GPU upgrade would improve things.
I have an older GTX 1060 6GB GPU and get the same choppy titles and transitions when using a UHD timeline but expect that with that GPU.
Rendering though is not too bad. My last video was shot in 25fps 1080p C-Log to Pro Res 422. No proxies needed. Project was graded and upscaled to a UHD timeline using Super Scale. Rendered to UHD h265 the 17.5 minute video took 39 minutes from start to stop.
Your 2.5 hours seems excessive.