What cables to use.

HDMI.

May or may not make a sonic difference over optical (depends upon the quality of the TV/cable provider), but you will be good to go with any improvements down the line.

Think they are around the same price, so HDMI.

If you shop Amazon or Walmart and would like something inexpensive look @ Monoprice HDMI’s.

This said, I'm not really into TV but the Monoprice HDMI I use to connect a DVD player works fine (picture/sound) with our TV.

DeKay

15’ should not be a problem for a decent HDMI cable.

I’ve used a 30’ Monoprice a few times to directly connect our Internet modem to the cable box (usually run WiFi, but it craps out from time to time) and it worked fine.

This said, our previous and current TV cap out @ 1080P, and like I said I’m not picky about TV (it just needs to look/sound OK).

DeKay