When I use Voice Chat for more than an hour, app becomes slow, unresponsive. I used the VC for more than a month with this issue and it is still there. The more I keep VC active, the more app becomes unresponsive and slow. VC may slow down the app even in shorter periods (less than hour), but it is probably not noticeable, so, I would suggest keeping it for more than an hour to reproduce it.
Telegram macOS 7.7 (215786) STABLE, MacBookPro16,3, 11.4