Changing sprockets on Shineray X1

[VroomVroom]

14 I think is biggest you can easily get but look in taobao I think I saw some!
I have 14/43 that's about the max it will pull without loosing a lot of hp
Revs lower same basic speed and slightly less pick up but not much
Mine what same as yours and 5th at 50km
Revved okish at 80km but anymore was high rpm
Now it's pretty good

I went the parts market and they didn't have suitable sized sprockets so I gave up.
I'm not sure what sprockets would be suitable for my bike on taobao. The ones advertised for my bike don't seem to offer any options.