Chess takes a long time to get good at. You "only" played 441 rapid in total, and while that seems like much, it's not. Unfortunately chess is an extremely time consuming habit. I would recommend at least 100 rapid games a month, + puzzles + analyzing games. Last month you played around 12 rapid games, I am sorry, but that's just not enough. I wish it was, but it just isn't.
Tyler1 (streamer) played around 4000 games in half a year, in that period he "only" improved from 600 to 1500. He had to play around 2000 more to get to 1900.
Also your puzzle rating is only around 900. Wayyyy to low. You need to boost that to about 1000 above rapid rating. If you want to be 1500, you should aim for at least 2500 puzzle rating imo.
Don't worry too much about your clock. I am working on a script that shows time consumption, and basically you win most of your games where you have more than 60 sec left. Plenty of the games where you are down on time, you still win. Don't worry too much about other people moving fast.
Also, you win rate for last month favors white pieces, but you are not doing well with black. Might want to look at that.
From looking at a few games, perhaps also resign later. You seem to resign because you make a blunder or think you made one. Don't resign before the actual position requires it.
Like I have just seen In my previous couple of games, I failed due to my inability to calculate what seemed like easy moves. Not even 7 minutes was enough for me to calculate a critical position where I was afraid of getting checkmated, or previously where my queen got almost trapped. I failed and only managed to calculate what happens if I get attacked by the rook, but instead opponent surprised me by attacking by a different piece that I overlooked was even a move. When analyzing the game it seemed not at all that difficult. It just seems like I am facing the problem of simply being too old to learn calculation. Like previously someone pointed out, all these 10 year old kids outcalculating older people. It seems laughably easy to calculate when I see even more complex positions in a video, but my ability to actually calculate something 10 times easier is simply missing.
Is is about brain plasticity? It seems like the kids have an enormous advantage there.
I think it is simply time to quit as my ability to calculate doesn't seem to improve and in fact drops below what seems very basic. I thought 15|10 clock time would work for me, but many times, again, I can't even calculate 3 basic moves before running out of time. Opponent, again, laughing at me with 15:15 on the clock on average. Elo seems similar to mine, so I don't know what I am doing there and how they find the brilliant moves in 15 sec each.