I can't tell if it's Quest or maybe something in my code that's lagging this really bad for me.
EDIT: Please try again, I uploaded the wrong file the first time.
I'm also using Pixie's Scope Library
Second Inventory: viewtopic.php?f=18&t=3789

It isn't laggy for me at all, but I did get this error:

Error running script: Error compiling expression 'object.quantity > 1': Unknown object or variable 'object'

Same Error, running over and over.

Sure, there is a strange timer named stack_inventory. Remove it and it will work.
Is it really necessary to import all this base functions into your game?

Yes because I created something similar to the Stackable library so I had to edit certain things like the Give and Take commands

OOps, I just realized I uploaded the wrong file! Here is the actual file I want tested

you should post your used libraries, too

Done and done

Did not lag for me, but I do not have main.js, so it might be different.

I did notice you have a timer called volume_quantity, that is iterating through every room and object in the game, every second. That is likely to have an impact, especially if you put your game on-line. When will item.unitvolume or item.quantity actually change? Could you not just set the value for one item when that happens (use a change script perhaps).

Try setting volume_quantity so it does not start, and see if the game still lags. Might be worth stoppng the other timers too to see what happens.

I got rid of a timer that was running faster than 1 second per a tick (using Javascript) and it seems to have gotten rid of the lag.
This game won't be directed for online play anyhow since it's going to be a big project.