I need more information to help you. Saying your game is laggy is not specific. What causes the lag or even what you think causes it would be helpful. However, I can give some tips:
Several Tips
Here are some tips to reduce lag:
Remove excess parts. A lot of parts can cause significant lag, especially on lower-end devices such as phones and tablets.
Remove memory leaks. If you have memory leaks in your game, lag will build up over time. This happens when you do not remove references to objects.
Remove excess textures and meshes. If you have thousands of textures, this can also cause lag. Make sure you use textures smartly and not for 6 sided objects.
That’s about it. If you have any further info, I can help more.
There are some finnicky and technical method to detect excess parts or overly dense details in certain area. To use this method, read from Performance. Especially under the Workspace tab. Once there, I think there was something that randomly changes numbers(can’t recall it correctly). These numbers changes accordingly to how dense the environment is.
If you were in a densely detailed area, the count rises to thousands. If you’re on a baseplate without any details, I believe it’s usually around 60 to 80 in count.
Optimization of building requires some thinking about alignments of each part. If you have two parts aligned neatly and the parts between them is not visible, you should merge them into one part instead.
Probably Script Performance
Expensive loops are not really good for a game, because these loops can cause awful amount of damage(leaks!) to the memory. The expense of a loop is determined on the code’s functionality.
Also long intervals sometimes cause memory leak. This is due to the reference is still in the table, which is created by, for instance, a player joining and data is cached. This is already mentioned in the previous post above by REALTimothy0812.
Probably Graphical
High definition textures or high poly count of a mesh can cause lag; high memory increase. If the graphical isn’t important, you should try to degrade the texture by reducing the resolution of them.
Try Unioning some parts, or setting the render fidelity of unions, meshes to automatic, also If your game has lots of lets say stoplights If there is one script per stoplight then Of course there will be lag!, making so there are one or two script(s) that manage the stoplights is more efficient and will reduce lag. One thing that can cause lag is the fact that there are lots of parts in your game. Try enabling streaming enabled, or reducing the amount of parts that are in your game.
Also, try to make sure your graphics settings in studio are tuned up!
Go to File>Settings…>Rendering>EditQualityLevel
And set that to automatic Or better yet Set it to the lowest setting possible.