Probably it wont be possible.For MV( and most HTML5 Games) there are only 2 options for graphics renderer: WebGL(Which is a Graphic API based on OpenGL) and Canvas(HTML5 Element to draw graphics). Dynamic shadow is something complex to create, and canvas probably wont handle it well(or wont handle at all).
More information:
https://en.wikipedia.org/wiki/Canvas_element
https://en.wikipedia.org/wiki/WebGL
But being honest with you, i must say that nowadays there are many phones out there that support webgl very well. Even my Vibe K5, wich has an snapdragon 615 + Adreno 405(made in 2016, may cost U$100 or less today) handle webgl well. With time, more and more phones will support it.
This lag of yours must be not because of WebGL, but because of parallel processes, map size or something like that. Phones are
extremely weaker than PCs.They have Less and slower Ram, slower GPU, slower CPU,many software limitations,etc. For example: my old R7 260X has up to 1971GFlops/s(1,9TFlops/s) performance, while Adreno 540(The best mobile GPU for android, until Snapdragon 845 comes out) has 567GFlops/s(I couldn't find information about Gtexel/s, GPixel/s,etc But it must be around 1/3 to 1/4 the amount of my card as well). This means that the BEST of the BEST for android can't even be compared to a PC which parts were made in 2013. So you really must make your games with focus on mobile limitations if you wish to port them for mobile.
Try to avoid using parallel processes(use 1 or 2 per map, max), try making small maps, don't use huge images when using "show picture",etc.
