How to fine tune the Client Side Script?

I have a scenario where I have customized the Sales Order Form and added too many fields and columns due to the requirement of the business.

Now, there are so many validations and code which is running at client end and cannot be run at the server side, and I am sure only this is the reason that the Sales Order Form has become slow.

Like I have 10 tables and summary of those 10 tables should be updated in the 11th table and I am doing it using the client side script, but that is making the process slower because data has not been saved to the tables yet and if I pass the each value of each table and use the server side script then it will again be the same.

Any solution/workaround for the same?

Note: In my understanding all the JS code runs at the client side not at the server side.

Ruchin Sharma