Some how what ever ZUN did to his DX3D file setting, few people, like me suffer some of his dojin game just got framerate lock at 20FPS or 15FPS (NOT cost by ingame 1/2 Frame or 1/3 Frame setting)
Here is how I got it fix, but it not permanent, everytime you reboot your system you need to do it again.
Example: 东方神灵庙 th13
1. Go to game file find th13.exe
2. Mouse.Right click - Properties
3. Compatibility
4. Compatibility mode Set to Windows XP (Service Pack 3)
5. OK than Run the game (For my case at this point the game will be at 60FPS at start and gradually drop to 15FPS or even 0FPS)
6. Go to Properties again
7. Cancel the Compartibility mode to normal my case Im windows 10
8. Run the game than it`s stable at 60FPS (If your rig is really relic low end maybe you just can`t reach 60FPS)

PS: After your doing this every ZUN`s dojin game suffer the same problem will be all right (If you play th18 东方天空璋 now you will find it work at 60FPS too), for this time only, if you reboot or shut down your PC you need do this again. (So I think it`s maybe a problem that windows DX3D setting got conflict with ZUN`s game DX3D setting)

不晓得ZUN神做了什么，少部分人，包括我在内的人，ZUN神的很多同人游戏都会出现被锁帧的情况，会被锁在20帧，15帧。（并不是游戏设置1/2帧率或者1/3帧率运行导致的）
我姑且在这里摸索出一个管用的方法，不过因为无法永久有效改善，所以每次重启电脑之后以下的项目你都需要重新做一遍才能正常60帧游戏。
举例：东方神灵庙 th13
1. 到游戏目录找到th13.exe
2. 鼠标右键下拉菜单---属性
3. 兼容性
4. 把兼容模式设成 windows XP (Service Pack 3)
5. 之后运行游戏（我在这种状态下，刚进游戏是60FPS不过会逐渐随时间掉帧，无限去逼近15帧甚至能掉到0帧去）
6. 关掉游戏，再去属性里面
7. 取消兼容性模式的勾选，变成默认就好了，我的情况我默认就是win10
8. 再启动游戏就能正常60FPS运转了（不过如果你用的是个性能超级Low的古董电脑或者有什么问题可能会到不了60FPS）

附录：只要你在任意一个出现这个问题的ZUN神游戏执行过这个步骤，你就会发现，其他所有也有这个锁帧问题的ZUN的游戏就都正常了（意思就是你现在再去玩天空璋就会发现你没改动过但是天空璋也正常了）。不过就只能在这次开机期间有效，重启电脑之后你还得搞一遍才能正常。（所以我觉得貌似就是window的DX3D设置文件和ZUN神自己调的DX3D文件有冲突导致的）