While I agree that low gears are your friend, you aren’t even trying hard I hate coasting down hills so I do the 20 tooth inner with a 46 tooth outer. Your low is okay (18” gear) but it’s not a 15” gear. I have a 46/34/20 with an 11-36 cassette. Here’s mine compared to yours. I can crawl up hills but I can also fly down the other side.