Extremely long render times with long file

Hello, i have a 7 hour movie which takes about 16 hours to render to you tube H264 codec. Now i have split the edit into two shorter ances like 3,5 hours each and the render times are only 2 hours each. I am wondering why the render time becomes so extremely long with the longer clip, is that maybe because of to little harddisk space to render the long file?

Source matterial 1920 *1080 mp4
Hardware macbook pro i9 64gb ram
Output coded youtube full hd 
Sequense has some after effects clips with dynamic link, not heavy just some moving titles

Thanks