You are asking really tough questions. First consider small cell lung cancer treatment has dramatically improved very recently. The two means that should interest you are precision radiation (you'll likely have a form called SBRT to deal with the brain met) and immunotherapy. Here is information about precision radiation treatment for all types of lung cancer (including small cell). Here is a very recent advance on adding the immunotherapy drug atezolizumab to the standard chemotherapy regime for small cell. So, for the first time in perhaps 3 decades, effective treatments are in play for small cell lung cancer. Note also, precision radiation can also be used in place of surgery to address the tumor in your right lung. Be sure to ask your doctor about adding immunotherapy to your conventional chemo and addressing both the lung tumor and brain met with precision radiation.
We have small cell survivors on this forum who've been successfully treated. I wouldn't know their ages. I can't begin to answer if treatment is worth it for you. It was and has been for me.
Stay the course.