Is there anyway to turn down how fast Rampant scales?

Right now I find I'm fighting L10 Leviathan biters around half way through my k2 playthrough. I have enemy level up to 10, so it's quite overhwhelming and I can only survive by making construction robots invulnerable (which feels lame).

I imagine this is because K2 takes longer than a vanilla game. However, I can't really find any setting to say "slow down the rate of growth". Can anyone help me figure out how to slow do the advancement of the biters?

What evolution %% are you at in your playthrough now?

Many things can be named as "advancement of biters" . Do you mean overpopulation or big squads (they grow in size and activity with evolution), or too strong biters produced by nests?
The last one can be addressed by tuning in Settings/Mod Settings/Startup "World: Ending enemy level" - out of map, setting change will apply after factorio restart for any loaded gamesave.
Overall activity can be reduced via Settings/Mod Settings/Map "AI Difficulty Scaling" - must be changed after loading your game and then press "Confirm" and "Back". Setting is stored with gamesave (loading old save will revert setting change).
Big size of squads is changed via mod files editing and is also dependent on evolution %%.
Overpopulation is like positive feedback in physiology - it leads to more activity, way more difficult game if you allowed biters to nest too close and too dense. A bit of Rampant balance issue maybe. Crush them with all resources available - it will pay back in less ammo consumed later on defense.

Evolution is like .9 or something, half from pollution (which was minimal) and half from biter bases (which was normal).
I do not mean overpopulation or big squads. Those are cool.
I do not mean World Ending level as Krastorio gives you some very powerful end game tools and I want the biters to be competitive.
I do not mean overall activity. I like the aliens attacking and doing their thing.

What I'm talking about, is ideally I would be fighting the strongest biters at the end of the game. This means when I get powerful tools with Krastorio at the end of the Krastorio tech tree the biters would be sending L10 biters at me (Leviathans). What is happening, is they are sending these END GAME biters in the middle of my tech tree. So I need to slow down how the biters advance, to ideally be twice as slow (Is this the evolution level?). However, I could not find any option to do so.

0.9 is endgame evolution level. Yes, evolution value is a main factor for biters tier.

Reducing spawners destruction evolution factor in game map settings at game start could help. Default 200 is way too much for Rampant, especially if high density of original nests was set (over 200%/200%) - it provokes additional nests generated as reaction to player's aggression. Check other threads in mod discussion, especially about Rampant 1.0 release. Recalculating existing evolution could help you.