If it's a rant and people are watching it just to listen to you talk about stuff rather than to get a specific answer to their questions then honestly length doesn't matter so much.
My advice is, if viewers are coming to your video for a specific purpose (to learn something, get an answer, find something out etc) then get to the point as quickly as possible and don't add in any filler. Even if the video ends up just being 2-3 minutes, if that's all you need to get the viewer their answer, then your 2-3 minute video will perform much better than someone's 15 minutes of beating around the bush.
If it's entertainment, which can come in multiple forms, a show, gaming videos, vlogs, or just talks/rants - then duration doesn't matter, and in fact I'd say you're better off with videos in the 10-15 minute range than shorter ones because the people coming to these videos are just here to be entertained/listen/watch and they just want to sit back and enjoy without having to change videos every few minutes. I'd say try to keep it around 20 minutes or less though since people are used to YouTube videos being much shorter than the stuff they watch on TV and even the people looking for entertainment sometimes are strapped for time, so ensuring they can at least watch a whole video in their sitting is still important - people don't like to have to pause and go back to a video at a later date to finish it.
So my advice is not to worry too much about shortening it. One thing I'll advise is be careful about how you advertise longer videos - ensure people know they're in for a long ride before they even click the video, or your retention rates will perform poorly and your search rankings will drop. I've stopped advertising any of my longer videos externally and just allow people to find them through my channel or search, and it's helped keep them ranked. Pay attention to your audience retention in analytics after the video is uploaded, if it's a gradual drop from start to finish then that's normal for longer videos. If a bunch of people are dropping off at certain points in the video take a look if you said anything off-putting, and if you didn't the first of those big drops is probably a good duration to use for future videos of that style. (i.e. if there's a big drop at 13 minutes, try keep future videos around 13 or less)
As for actually making videos shorter, my advice is just to plan out what you're going to say beforehand if you want to cut down on time. Focus on how you're going to convey your point in a way that more people will understand the first time around so you can spend less time on each subject you cover. Splitting the video without finishing the conversation is only a step less problematic than people having to pause and come back to the video mid way, since they're going to forget things that were said if they come back for part 2 later rather than watching it right away. If you do decide to split videos, plan out how to segment the rant/conversation before you make the video, and cover one subject in video one, and another in video two, that way the videos are somewhat standalone and can perform well individually too.
Hope this helps
