Need recommendations on 15ft speaker cables

The OP is already using 10 awg stranded copper speaker cables, which is plenty big for the run length.  Other than a few posters suggesting Canare 4S11, just about every poster has given a different cable recommendation.  BTW, 4S11 is actually a smaller stranded copper speaker cable than what the OP is using now, at 11 awg when configured in star-quad geometry.  

At this point, he/she either jumps on the buy/try cable merry go-round or tries the Cable Company or others that will lend cables in order to evaluate which of many cable offerings he/she likes best, or if they even hear a reliable difference between cables.  A lot of us have done the buy/try route, but it is expensive and time-consuming.

@crustycoot 

My advice is...  Mogami, and Canare is another, both available from World's Best Cables on Amazon, see: Canare 4S11 or Mogami 3082 Once you are accustomed to these, you can try borrowing some Cardas, Audioquest, Nordost, Transparent or other higher priced cables.

Good advice: Mogami/WorldBestCables/Canare/Belden (actual cable manufacturers) or other Speaker cables on Amazon. Read the descriptions/diagrams and reviews carefully. And you can return easily!

Bad advice: Higher priced cables from resellers so called major brands (they buy or import cables and dress them with thick jackets and you pay 10x 20x more

Very very happy with a recommendation I got here, fantastic value: https://www.thecableco.com/straight_wire.html

I have a friend, a former concert pianist, who has one of the best systems I've ever heard.  He has some pricey interconnects and even a power cable or two, but I asked him once what speaker cable he was using, it looked sort of rugged.  He said, "You won't believe me if I tell you."  So he told me anyway, and I tried it, and it's the best speaker cable I've ever heard.  I've sent some to friends and they love it too.  It's 8 AWG stranded THHN combined with (yes, really) 18 AWG 5-conductor copper sprinkler cabling, with one conductor snipped and the other four twisted together in pairs for positive and negative.  You can parallel the two or use them separately for bi-wiring, which I do--the 18 AWG for the highs and the 8 AWG for the lows.  For termination I use large copper offset lugs, snipped to make spade lugs.  Or you can get large-size screw-on banana plugs.  I strap them together with cable ties.

I like Blue Jeans cables, especially their interconnects and digital spdif, they just sound NORMAL.  But I like this rig better than their speaker cable.  Cost about $100 for a 15 foot pair, and you can buy both cables in bulk from Amazon and save some money.  How do they sound?  Big, rich, smooth, open, plenty of detail but absolutely no fussiness or phasiness.  That's my free tip for the day. ;-)

I can highly recommend the Anti-Cables 4.2 Flex speaker cables, best "pre made" speaker cables that I've ever tried.....I use them on my Clayton Shaw Caladan and Buchardt Audio S400 MkII speakers. They come with a 30 money back guarantee policy, and a bunch of vendors use them at audio shows

If you are willing to go down the DIY avenue, you can make some incredible cables with screw on connectors. Neotech, Furutech, Oyaide, or VH Audio; and some WBT or Furutech screw on connectors.