Well you say you feel great, but then you have to stop after 10 mins of exercise. This isn't great I'm afraid :(
Let me explain something about your exercise and pain. Your cardiologist should have done this. When you feel chest pain, it's bad news. Your heart muscle is crying out saying I'm suffocating and being damaged. When you stop and relax, the pain goes away, but this doesn't mean the heart cells have recovered. It can take some time. Keep stopping and starting in bursts is going to cause permanent damage over time because when heart muscle dies, it stays dead. So, you should avoid all forms of exercise which are too strenuous for your heart. A slow gentle walk each day is fantastic. So is gentle swimming. It will still burn the calories. With regards to your collaterals, I'm not sure which research your cardiologist has read. The only way I know of that your collaterals will open, is if the blockage worsens because it's all based on pressure differences in the coronary arteries. This is how EECP forces them open. Nothing you do will reverse your situation, but changes can certainly stop it getting any worse. You have been told you can't have a stent, but if medication is not working enough for you to have a quality of life that you can enjoy, then bypass is probably an option. To simply send you away saying you will develop collaterals is, well, I think I will stop here. I strongly suggest you get a second opinion.