While Ubuntu itself doesn't participate in the alpha releases but rather focuses upon the quality of their daily ISOs, the opt-in flavors of the Ubuntu family that does do these early development releases have announced their 15.10 Alpha 1s.

Ubuntu 15.10 and family are codenamed the Wily Werewolf and today is the first development milestone for Kubuntu, Lubuntu, Ubuntu MATE, Ubuntu Kylin, and Ubuntu Cloud.

If you're interested in these alternative flavors and don't mind that they aren't yet production-ready, you can try out the releases with the download links from the joint release announcement. As the Ubuntu 15.10 cycle progresses you'll be able to find all sorts of fresh Ubuntu 15.10 Linux benchmarks on Phoronix.