Hey,
I’m 99% sure I know what the problem is and I hope I can help you because there is a solution to it. SO basically I’ve been developing on my MacBook for years and it worked fine until roblox studio had multiple updates. Through time it became a “nightmare” I couldn’t move a block without having my laptop freeze for 5-10 seconds. I’ve then downloaded a RAM checking app (not RAM thats impossible it’s a checking App) and I noticed that roblox studio took like 70% of my RAM once I opened it. (That’s what the App said) I then started closing all other Apps such as Spotify, Google Chrome, Discord (And everything else). I only had roblox studio open and it worked much better. One day which was about a year ago another update came and I wasn’t able to open roblox studio on it anymore. My MacBook was from 2014 or 2015 I don’t really remember. I now changed onto a normal windows PC and it’s killing it. I’ve told myself that I’ll never ever again buy a MacBook or iMac.
Anyways here the solution again: Close all other Tabs Discord, Spotifly etc and the lag should get reduced. It should work!
I hope this will help you! 
- Cheerful