to the forum Barbarian Coug,
The 3150RL is listed as *STOCK ONLY*, which means this particular floorplan has been discontinued, and only the
"current stock" will be available. Yes, the 3155RL is a new floorplan for the model year, but that doesn't necessarily
indicate that it's replacing any specific model #. It's not uncommon for manufacturers to add/drop models from year to year.
You can see (& compare) the Montana model changes, here:
http://www.keystonerv.com/montana/#/floorplans
Hope this helps & happy shopping,
Terri, the Chevy co-pilot