I don't have a Youtube channel but I have taken many Marketing courses and watched a lot of Sims videos on YouTube so I can offer you some suggestions.
1. Tags: Using the right tags on YouTube is very, very important as doing so will help increase your ranking in search results. Please Google some articles about tagging and SEO. You can also check the tags that famous Simmers are using for some ideas. On Chrome, you can do this by
-Opening a video's page, then right-clicking on the page (not the video) and selecting "view page source"
-Another tab will open that is full of complicated-looking html data. On the upper right-hand side of your screen, click on the 3 small dots and then click on "Find".
- A small search bar will appear. Type "keywords", and you will be able to see some of the keywords used.
I used this method to check the tags on some of your videos.
For your "WILL YOU MARRY ME?" (HALLOWEEN MACHINIMA) video, your tags were:
"breaking news, news, like, comment, channel, free subscribers, free views, free likes, get famous, how to get famous, how to get popular on youtube, sims 4."
Other than the "sims 4" tag, you shouldn't use those other tags in the future because they are not relevant to your content and therefore won't improve your search ranking. A few examples of better tags for that Halloween video are "Sims 4 Halloween", "Machinima" "Sims 4 CC" "Sims 4 Custom Content" "spooky" "Thomas TV" and "Sims 4 Halloween CC".
On several of your other videos (like Autumn Bedroom), you used these tags: "katy perry, katy, perry, video, breaking news, news, like, comment, channel, free subscribers, free views, free likes, get famous, how to get famous"
I'm not sure why you chose to mention Katy Perry in so many of your tags, as I couldn't find Katy Perry in those videos, but that might be one of the reasons for your low watch times. A few people watching videos by other YouTubers about Sims Katy Perry CC might have seen your videos in their suggested section, clicked on the link, realized it had nothing to do with Katy Perry and left. So don't add a Katy Perry tag if there is nothing about her in your video as it is not an accurate description of your video's content and it may attract the wrong audience.
For your City Living Let's Play, I would suggest changing the tags to stuff like "sims 4 city living, sims 4 city living gameplay, sims 4 san myshuno, sims 4 city life, sims 4 apartment".
For CC videos, I would suggest: "Sims 4 cc, sims 4 CAS, Sims, Sims 4 tumblr (or wherever you found the cc), sims 4 tumblr cc, Sims 4 custom content, MaxisMatch (if used)"
2. Titles: Having eye-catching titles will increase the number of clicks on your videos. For your City Living series, instead of just naming your video like "THE SIMS 4 | CITY LIVING LP - PART 10", you should try to add a few words to the title describing what happens in the video. For example: THE SIMS 4 | CITY LIVING LP - PART x: Karaoke Contest or THE SIMS 4 | CITY LIVING LP - PART x: Trying Sushi or THE SIMS 4 | CITY LIVING LP - PART x: Wedding in San Myshuno! This sounds better as it is more attention grabbing. It will also help viewers remember which of your videos they have already watched. If they see "Karaoke Contest" they are more likely to remember that they have already watched that video than if it was just titled "Part 9".
For CC videos, instead of just naming them "CC Shopping #5" you should mention your best finds from that video. For example, something like "CC Shopping | Maxis Match Hair" or "CC Shopping #5 l Sparkly Eyeshadow" or "CC Shopping #5 l Luxury Sofas!" would stand out more.
One of your most popular videos is "WILL YOU MARRY ME?" (HALLOWEEN MACHINIMA) and I think that is partly due to the title.
3. Descriptions: Instead of just putting the video title and "click to see more" in the first part of the description, you should be writing a brief summary of what is going on in the video. A couple of sentences will do. Using relevant keywords in those sentences will help your video rank higher in searches.
4. Thumbnails: The thumbnails from the last few months look very good! I think you should add a couple of words in them though, like "City Living" or "Speed Build". I feel like that would get more attention than a beautiful but wordless thumbnail.
5. Comments: You can increase peoples' awareness of your channel by commenting on other Simmers' videos. Don't just say something generic like "Great video!" though - write a couple of sentences about specific things you liked or say something witty.
6. Social media: I notice that you have your social media listed under your videos but not linked. You should have clickable links to your Twitter and Instagram pages under all your videos so that your fans can access them easily. People tend to be lazy and many won't bother to copy and paste social media handles into Google.
When I googled your Instagram and Twitter I couldn't find your profiles at all. :o I got results about an English painter from the 19th century called Thomas Sidney. And when I searched the Instagram app I couldn't find it either. I did see a few Thomas Sidneys, but they didn't appear to be related to the Sims. I think you should consider naming your Instagram and Twitter ThomasTV instead as that would really help with your branding.
I hope this helps you and you get more viewers and subs! :) You have good content- you just need to work on your marketing!