How to fix a comment timing out problem

Hello everybody, I’m experiencing a bit of an issue in the WordPress site I’m programming and wanted you to give me some advice.

Well, this site has over 400K posts (yes, we managed to fix it by calling everything from de DB, so works 100% well and even faster than regular sites)and the problem is that when an user or visitor tries to comment the site dies. 504 Error!! But only under that circumstance, otherwise it works perfectly fine.

So, we came up with a way to fix this (theoretically). Is it possible to move the comment count column away from wp_post, to another table??? (such as a “Most viewed post” table) so it doesn’t generate extra calls and avoids the timing out.

If this isn’t possible, what solution do you recommend for solving this problem? I know there has to be one, because in our project list fixing our beloved comments is a must.

Any of you ever dealt with something like this?

Any response is welcome, I very much apreciate it!!