I'm not exactly sure what you're looking for, but if it is to pare down the landcover layer to only water/not water, then you can do something like the following, which selects only the LC_Type1 band, loops through each image in the image collection and creates a boolean output for whether or not the band value equals 17.
var Landcover = ee.ImageCollection("...
Pulling an uncompressed and untiled geotiff (even a small one like 128Mb) is going to be slow.
You should process the GeoTiff using the advice in GeoServer on Steroids (video) or Paul Ramsey's GeoTiff Compression for Dummies. This will probably make your tiff small enough that the network transport cost doesn't overwhelm your reading time.