Does the length of the Cable matter?

Yes it matters. Do to the low output of the TT. Phono cables are constructed differently than standard interconnects. The shorter the better. 1.5 meter length would be the max length to use and that length would be based on a very high quality cable. I’m not sure you can even buy a phono cable at 15 feet.

‘You will get sound out of the TT at 15 feet but the sound quality will be diminished.

‘Give it a try. If your happy with the results that’s all that matters.

Joe Nies

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Since your TT has a phono preamp built in, there is no problem going with a 15 foot cable. It’s a line level output from the phono preamp to your preamp line level input.  If cable was coming from TT (no phono preamp built in) to your preamp phono input then a short phono cable should be used for best results.
‘Joe Nies