15 minutes of just sitting in the calm quiet is proven to reduce stress hormones in the body by helping regulate the hypothalamic-pituatary-adrenal (HPA) pathway. 15 minutes of quiet every day can work wonders on your mental and physical health. Deactivating the HPA pathway reduces the stress hormones in your system, which reduces every bodily systems stress reaction. This can help your mood, obviously. Anxiety, depression, irritability, all responses to stress. It can also help with autoimmune issues, though. Stress hormones cause your immune system to go into overdrive because your body is expecting to have to deal with a wound as a potential source of infection. Lowering those stress hormones has been demonstrated to help with autoimmune disorders like lupus, fibromyalgia, psoriasis and others. It's said that we operate in two modes: fight or flight, or rest and digest. When you're stressed, your body moves resources away from your digestive system. It's basically saying "We dont have time to digest food right now, we gotta run away from this bear". If you're stressed all the time, you're always running your digestive system inefficiently. So regulating the HPA pathway has been correlated with improvements in shit like Crohn's, colitis, IBS and other digestive issues. Constant stress boosts your heart rate, constricts your blood vessels and increases your blood pressure, so regulating the HPA pathway can lead to decreases in the risk of cardiovascular diseases.

Thing about sitting quietly in a calm space is that a lot of us, myself included, will fill that space with thoughts that just cause more stress. Luckily for us anxious folk, meditation exists and is quite literally the culmination of millennia of smart, dedicated people trying to solve this exact problem. There are tons of resources online where you can learn how, many of them are free. They'll teach you how to detach from stressful thoughts and situations, how to stop agonizing over what's already done and being terrified of what could happen and just acknowledge what's going on right now. Try it. If I'm totally wrong and you hate it you're only out 15 minutes.

Tldr - stress hormones make your whole body go into emergency mode. Emergency mode is good during emergencies, but not good all the time. Bringing your body out of emergency mode when there's not actually an emergency helps pretty much every part of you be healthier. You can bring your body out of emergency mode with 15 minutes of sitting quietly in a calm space. Meditation can help you establish that calm space.