We've considered the possibility of adding sound-deadening curtains to divide off the back of the long room where there is a bar top. Would bring things forward maybe 10ft (as far as a back wall is concerned)
How much impact would that have on the listening experience?
Curtains would have no effect on low frequencies, so it won't be like moving the back wall forward. Rather than attempting to change acoustics by shortening room length, easier to place the seating so that it is less affected by acoustical problems.
I'm sure you've blown across an empty bottle and made the air in that small chamber resonate (make that booooh sound). If you enlarge that small chamber to the size of your room, the air inside will still resonate (of course at different frequencies than the empty bottle). The 32-foot length of your room is going to result in resonances (room modes) at specific frequencies: 18Hz, 35Hz, 53Hz, 70Hz, 88Hz, 106Hz, etc. The first 4 of those length modes are mapped on the graph below:
Any number with Hz after it is a problem frequency. Each problem frequency is colour coded, so you can see the locations of its peaks & nulls. The other numbers are distances from the front wall.
Notice that the midpoint of room length (pretty close to the 15-foot distance you were planning on sitting) has the worst frequency response: everything is either peaking or nulling. Also notice that all the nulls are at even divisions (half, quarters, sixths) of room length. To avoid them, it's a good idea to place the listeners' ears at one of the odd divisions (thirds, fifths) of room length, where things aren't all-peaks and all-nulls. That's why I suggested putting the listeners at 13 feet from the front wall, because it was one of the odd divisions (2/5ths) of room length.
The smoother bass response will give a big head start to the room correction system in your receiver. And it's free (doesn't cost anything to move the seating a couple feet forward).