after update stackblitz dependencies to latest, this bug appear on it, so under version 13 it works normal, but under latest 15 it slow down.
i found this in change log:
icon: re-enter Angular zone after icons have been loaded [#7719] [754ded6]
maybe it happens because of this fix?

The re-enter Angular zone commit was a forward fix for the previous issue where icon re-rendering (where detectChanges() is called) affected other parts of the template because it was called outside of the Angular zone. I was trying to reduce the change detection cycles triggered by a "load + render icon" flow. I could only reduce this number by wrapping changeIcon into runOutsideAngular so any asynchronous stuff happening while the promise is being resolved doesn't force Angular to run tick(). The issue you're talking about has existed before any zone-related changes have been made to the nz-icon directive.

I tested the code locally and it takes 23 seconds for me to render after clicking "Reload". I was able to write the solution where it takes only ~7 s to render:

That's not the best result. But this is x3 boost compared to 23 seconds.

I had to edit the code directly:

// ng-zorro-antd/fesm2020/ng-zorro-antd-icon.mjs

let scheduler = null;
class Scheduler {
  constructor(ngZone) {
    this.ngZone = ngZone;
    this.callbacks = new Set();
    this.scheduled = false;
  }

  schedule(callback) {
    this.callbacks.add(callback);

    if (this.scheduled) {
      return;
    }

    this.scheduled = true;

    requestAnimationFrame(() => {
      if (this.callbacks.size !== 0) {
        this.ngZone.run(() => {
          for (const callback of this.callbacks.values()) {
            callback();
          }
          this.callbacks.clear();
        });
      }

      this.scheduled = false;
    });
  }

  static create(ngZone) {
    return scheduler || (scheduler = new Scheduler(ngZone));
  }
}

class NzIconDirective extends IconDirective {
  constructor(
    ngZone,
    changeDetectorRef,
    elementRef,
    iconService,
    renderer,
    iconPatch
  ) {
    super(iconService, elementRef, renderer);
    this.ngZone = ngZone;
    // ...
    this.scheduler = Scheduler.create(ngZone);
    // ...
  }

  changeIcon2() {
    this.setClassName();
    this.ngZone.runOutsideAngular(() => {
      from(this._changeIcon())
        .pipe(takeUntil(this.destroy$))
        .subscribe({
          next: (svgOrRemove) => {
            this.scheduler.schedule(() => {
              this.changeDetectorRef.detectChanges();
              if (svgOrRemove) {
                this.setSVGData(svgOrRemove);
                this.handleSpin(svgOrRemove);
                this.handleRotate(svgOrRemove);
              }
            });
          },
          error: warn,
        });
    });
  }
}

This is the most basic scheduler implementation. In practice we should be more flexible and don't allow the scheduler to keep more than say 40-50 tasks waiting to be executed. So if callbacks.size becomes greater than 40, we should flush callbacks and start scheduling again.

In my app it's come to the point where I have to replace icons with words or emojis even, because the performance for icons in lists or tables is just too slow.
Is this being worked on? Is there another issue that tracks the overall performance problems with the IconDirective?