Were you able to adjust the volume of your TV at 15ft away before you installed the Beam? Also, note the location of the Beams sensor. See the link.

https://support.sonos.com/en-us/article/ir-sensor-location-on-sonos-home-theater-products

If mounted extremely low below your TV the angle may be an issue.

Note that in general, when connected via ARC, the Beam receives its volume ‘control’ messages from the TV itself, and not directly from the remote.

This is slightly different when the Beam is connected to the optical output of the TV, which can’t carry CEC commands. 

Did you maybe put the Beam in front of the ir sensor on the TV?

Your Beam uses IR for volume, so distance and line-of-sight matter. Enable HDMI-CEC/ARC on your TV for reliable control without needing to aim the remote.