When you’re talking about speeding things up, there are many, many possibilities. If your table has a lot of columns, from what I’ve heard from other people, that might very well slow things down. But so could the imports of your server module, and other factors.
So it’s worth taking an overall view of the speed of server calls, and working out where your delays are. There are posts on the forum that talk about timing your imports and other factors.
To get back to your original question, your search iterator can be limited by rows, but not by columns. If you want to return a subset of columns, you have to build a list of dictionaries containing only those columns you want to send back to the client. You lose the lazy benefits of the search iterators, but later pages will load instantly. It really depends on how much data you’re processing as to whether that makes sense to do.
There is a feature request for allowing selection on a subset of columns that you can like to show support for: Client-readable views on a subset of columns
How many columns are in your tables?