Try resetting your game configuration to default by deleting gta_sa.set
If that doesn't help I might need more information from you in order to be of some assistance.
For example, where does this issue in specific occur?In what areas of the game?The game isnt discriminative towards LV only so there could be a specific area thats causing you to lag(it could be BB Acres, that area is known to cause major fps drops for no reason).
Whats your hardware configuration?
I mean theoretically anything can run this game but itll also come down to your system specifications to some degree.
Do you have any other apps running in the background?
Applications that run in the background consume resources which causes the game to run slower as the system has to allocate resources for other applications equally.Closing any applications you dont need can boost performance.
Do you have any mods/3rd party game installations?
Any unapproved mods or any mods developed by sketchy sites could cause your game to slow down as its either coded poorly or it could have another purpose such as being a virus.
Please consider installing a clean version of the game if you havent already, as not only does it make the game run as intended but it also ensures all players share the same experience.
Once you provide the above I could probably help you a lot more.