Cad file size or points limit

Hi there,
I was wondering if you can help with my query, I tried to upload contour from dwg file and got a message that there are too many points and suggestion box to reduce the tolerance. I couldn't find help on this topic to best approach this ie I tried to delete some of the contour lines that are not needed and purge the dwg file to reduce the size but still getting the too many points and the process will be slow message. And with reduction method not sure how much is it optimal size without losing too much tolerance.