Optimizing Arena Save/Load

[JustAnDev100]

Hello, So I'm trying to make a skript that will save an arena and load it. I need some help though. The first like a minute or two it works fine with 19.98 - 20 tps which is average for my server after a certain amount of time the TPS goes down a lot I mean like to 10TPS I don't want to use addons (At least try to don't use them) And I want it to load (Relatively) Big arena's

function saveArena(arena: text):
    set {_speed} to 0
    delete {revertlist.%{_arena}%::*}
    set {_height} to {minh.ww.%{_arena}%}
    loop ({maxh.ww.%{_arena}%} - {minh.ww.%{_arena}%}) times:
        loop all blocks within block at {ww.pos1.%{_arena}%} and block at {ww.pos2.%{_arena}%}:
            y-coord of loop-block is {_height}:
                add type of loop-block to {revertlist.%{_arena}%::*}
                add 1 to {_speed}
                set loop-block to red stained glass
                if {_speed} is higher than 75:
                    set {_speed} to 0
                    wait 5 tick          
        add 1 to {_height}
        wait 5 seconds
    revertArena("%{_arena}%")
function revertArena(arena: text):
    set {_bla} to 0
    set {_height} to {minh.ww.%{_arena}%}
    loop ({maxh.ww.%{_arena}%} - {minh.ww.%{_arena}%}) times:
        loop all blocks within block at {ww.pos1.%{_arena}%} and block at {ww.pos2.%{_arena}%}:
            y-coord of loop-block is {_height}:
                add 1 to {_bla}
                set loop-block to {revertlist.%{_arena}%::%{_bla}%}
                if {revertlist.%{_arena}%::%{_bla}%} is chest:
                    set slot 0 of loop-block to wooden sword
        add 1 to {_height}

If i remove the delay's the server would just crash. I already thought about the placements of block im doing in the saveArena part but i dont know how to show the progress in a different way if the block placement is causing the issuse can someone tell me how to display the progress?

Thanks alot!
If you can optimize the code / Make it less laggy (Prevent qrazy TPS drops) i will be very happy!

EDIT: The {ww.pos1.%{_arena}%} are locations also there is a little thingy build in that will fill chest with items when loading arena again
I want to use this script for Resetting a map.