have not been on a long ride yet
as I just got my 1800 in November. Early returns mirror those above...1500 has better storage. On long rides with touring seat (Diamond) I really liked my 1500.
The 1800 is definitely zippier, and the fuel injection makes easier starting. No judgement yet on the smaller storage; I have a trailer for runs of more than 3 days. the 1800 also seems to have a little better balance, and being about 100 pounds lighter is nice in traffic.
Ask again at the end of the summer, and I'll have a better answer.