That "shock" is from the PG then. It's a flavor carrier, but too high a PG ratio WILL give you a harsh throat hit. Some people like it, others don't. Why not try a 70/30 VG/PG mix at say 8 or 9 mg/ml of nicotine?
I'm pretty certain your issue is the PG, not the coil or wattage. I don't think trying the lower resistance coil is going to improve matters, only worsen it. You won't be able to vape below 35 watts, I GUARANTEE it.
If you have more VG in your vape, YOU WILL most likely be able to lower your wattage and still get a satisfying vape. Why not try it, you have nothing to lose, and a lot to gain.
You can also try nic salt juices if you think it's the nic. I use them because I do NOT like a harsh throat hit, they're a bit more expensive but they might allow you to get your nicotine higher.
It is PRIMARILY PG and Nic that offer the throat hit, and the higher wattages will only intensify that. I had a horrible sore throat due to my health when I quit smoking, and I found that nic salts improved things considerably.
I can guarantee that if you change nothing except the coil, you are going to wind up with EVEN more of an unvapable mess. MOST people who are sub0hming (less than 1.0 resistance coil) use 50/50 mix at the LEAST. Most people go even higher on VG.
You came here to ask questions, I am answering them, as are others. It was stated that the 0.15 coil would require higher wattages, and a lot of us think your wattage and your PG/VG mix are your PROBLEM. Also, you may not need more nic. If you can vape more frequently at lower watts, because your throat isn't sore, you may find you stabilize nicely.
You know, you can buy VG almost anywhere, so cheaply. Even Walmart carries it as do many pharmacies, if you want to know if PG is the problem buy some and add some to a tank of the juice you have and pay attention to differences. Yes, it will be lower nic, but the idea is for you to find out the right PG/VG ratio for YOU. Just make sure you get USP grade.
You are being given a lot of information and I know it's hard to digest. The 0.15 coil is unlikely to be helpful to you in this situation.....
Anna