after small checks i found out that in case of slow filling of channel lists the ListView.Add is the slowest element in the chain. I will try to improve performance of it first.
well, i submitted the patch for channel list in groups https://forum.team-mediaportal.com/...ls-filling-tvsetup-channel-list-groups-98092/ , but it doesn't eliminate the problem when for every channel in the list SQL query is executed, what in my case with 4200 channels is surely slow. I am not very good in C# and need someone's help on how it can be fixed.