Can you tell me what aspect is running slow? Is it the registration process? If so, is it with all social networks, or one in particular? Any other details you can provide on what is slow and what portion specifically is slow (like loading the social network login area or the step after you enter your social network credentials and the login to Joomla occurs) will greatly help us investigate further.
As for Joomla 7.2.4, that is an older release. The 8.0 release has numerous changes for multiple networks to improve compatibility. Many of those updates were aimed at Facebook after their privacy issues earlier this year caused a lot of changes to their API, but there were additional changes to LinkedIn, Twitter, Google and a few others as well to keep them up to date with each social networks changes. None of the updates should have a major speed impact, but should fix some compatibility issues you may encounter if you use the 7.x releases.
I hope that helps explain, but please let us know any details you can share.
Thanks,
Alex