Every, freaking, time I open Cydia, it updates Packages & Releases for 30 mins at least.
SERIOUSLY, WHAT THE ****?
It happens every hour and every day.
And it's pretty freaking annoying, because I know that there are many packages that are being updated, but why the hell does it take that long to update the index? Feels like it's terabytes of files that are updating.
Conclusion : Cydia sucks, I think I'm gonna change to installer 4.0
Do you have a lot of sources installed? Probably one of them is "timing out" so it seems laggy. Remove sources except for the defaults (BigBoss, ModMyi, ZodTTD, Telesphoreo) and see if the problem still happens.
You also have to realize that it may be like this for a little while as the repos are still getting hammered with the launch of the new untethered jb. there is a ton of traffic to the repos. And just a little further education it is the repos fault and not cydia's. The implementation of cydia is different than rock was as cydia does not store or host any repos. They are all stored and hosted by the repositories themselves. This was done in the event that the cydia server went down there would still be a way to get your apps and tweaks. Cydia is essentially a middle man that is just an interface to display what the repositories host.