Welcome to the forum, Bruce.
In very general terms, both are great choices. The 1500 has enough power to deal with long distance, heavy loads, mountains, etc. Its also more comfortable for the taller riders, 6ft+.
The 1800 is definitely the hot rod of the two. Its like a compromise between a 'Vette and a Mercedes. Taller riders often feel cramped because of the footpeg location, but that location is what lets the 1800 lean farther in the corners. Most riders will add highway pegs, back rests, bar risers......there is a variety ways to get more comfort, all the way up to a custom $1K seat. Other riders simply accept it and deal with it. Many riders really like the fuel injection on the 1800s.
If you're just looking for a safe comfortable ride from point A to point B, while carrying some luggage and maybe a passenger, the 1500 will probably satisfy. If you want all the latest tech and want to get to point B quicker, its the 1800. Don't get me wrong, you're not going to set new records on the Dragon, but those sport bike riding posers need to get out of the way.
If you keep up with the basic preventive maintenance, both bikes will last longer than either of us.
As the Fossil says, be patient and wait for the one that sings to you.
2003 GL1800/MotorTrike Adventure IDMWT#25x3
Ride often. Ride far. Ride safe and do much more of both.
Give a man a fish and feed him for a day. Teach him how to surf the GWOF and he won't bother you for weeks, maybe months
I'll be waitin' for you at the end of the road.
If everything had gone as planned, it would not have been an adventure.