Ideally you'd be doing a WC when ammonia is around .25ppm.
Plants remove ammonia, so ideally you may want to look for java fern, anubias and/or hornwort. Hornwort is especially good at getting rid of ammonia. However it can "melt down" when you fish add it, so quarantine it for a bit. Anubias and Java fern would be better choices for 1.5gal.
I think you should think about getting a 5 gallon with a filter, you can cycle it and then won't have to worry that your tap water has ammonia as much.