Disable IPv6 The Right (Debian) Way
With the native implementation in modern operating systems and software, IPv6 support has grown in recent years; however, the existing infrastructure just isn’t ready. As a result, a number of applications behave as though an IPv6 network is available, which not only wastes CPU cycles, but can also decrease application response time. More here
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Recompiling your kernel to not include ipv6 seems a bit drastic, easier to edit /etc/default/grub and add ipv6.disable=1 to the kernel loader like this: GRUB_CMDLINE_LINUX_DEFAULT=”quiet ipv6.disable=1″, saving the file and running update-grub. Problem solved.