You could try the JOSM editor[1], but iD is about as lightweight as it gets, so I am not sure if it would be much better. For what its worth, I use iD regularly without performance issues, but YMMV on older machines. Unfortunately, vector rendering and editing will tend to push browsers to their limit. This may be alleviated somewhat by the use of WebGL in coming years.
iD lightweight? It has trouble rendering a good block of houses when there is a lot of data whereas josm only gets into trouble rendering a small city or so of equally dense data.
[1] https://josm.openstreetmap.de/