Again, which ones? Diamond Back has 30 pages of tires in their catalog and many are made from widely available manufacturers, they just doll them up a bit with redlines, bluelines, wide whites etc. But, their base model tires are often BFG, Michelin, Cooper, Toyo, Nitto etc.
Many of the 15" series, even their extreme performance units, are still only S or T rated with 360 treadwear. Maxxis and MT are better designs than that. But if you want a 17 or 18 redline or wide white, they can hook you up.
Unfortuantly, there is very little in the way of ultra performance street tires in 15" sizes. Most tires in this size are all out race tires or long lasting cruiser tires with hockey puck style tread grip.
If you want some really wide, sticky, low profile 15" tires, Summit has Y rated, Pirelli P Zero 335/35x15 tires for $1075 each.
http://www.summitracing.com/parts/pir-0898600/overview/
If thats a bit too rich for you,there are the old design Michelin TB15 Comp tires. 295/45vr15, d.o.t. approved for only $635,
http://www.summitracing.com/parts/cok-71231/overview/.