I bought a 2014 model Shamrock 21DK and the mattress was really uncomfortable. I was staying at the campground at the dealer (Tom Johnson) and expressed my disappointment to the sales guy. The mattress in the 2015 model is a marked improvement, so we swapped a pair out of another trailer on the lot. I'm happy but the owner of the 2015 might not be.
Anyway, even with the improved mattress it's not like home. I can feel the springs through the top pad. We added a 2" gel foam topper. It made it more comfortable. It's still not home but we can sleep well with it. It's a compromise. After all, we're only glamping.