We were on Deck 10 on the Splendor. The cabins are forward, and we did feel some motion. We sailed in July when the seas were fairly calm. I purposely book high and forward cabins because we like to feel like we are on a ship rather than in a hotel. These are Spa cabins, so they are very nice. It was a very quiet location as well. Since it is one of the higher class cabins, it may be difficult to change cabins. I would suggest calling sooner rather than later if you decide to switch cabins.
On another note, I am very prone to motion sickness, so I start taking Bonine the night before we sail and every night of the cruise. If the seas are rough, or if we are going to tender, I take an extra pill in the morning as well.
I have never once felt the slightest queasiness. Normally, I cannot ride a ferry or any other kind of boat
without being miserable.
Good luck, and enjoy your cruise. We loved the Splendor!!