要调整RecyclerView中GridLayout的smoothScrollTo()方法的速度，可以通过自定义LayoutManager来实现。

首先，创建一个自定义的GridLayoutLayoutManager类，继承自GridLayoutManager，并重写smoothScrollToPosition()方法。

public class CustomGridLayoutManager extends GridLayoutManager {

    private static final float MILLISECONDS_PER_INCH = 50f; // 调整速度的因子

    public CustomGridLayoutManager(Context context, int spanCount) {
        super(context, spanCount);
    }

    @Override
    public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
        CustomLinearSmoothScroller linearSmoothScroller =
                new CustomLinearSmoothScroller(recyclerView.getContext());
        linearSmoothScroller.setTargetPosition(position);
        startSmoothScroll(linearSmoothScroller);
    }

    private class CustomLinearSmoothScroller extends LinearSmoothScroller {

        public CustomLinearSmoothScroller(Context context) {
            super(context);
        }

        @Override
        public PointF computeScrollVectorForPosition(int targetPosition) {
            return CustomGridLayoutManager.this.computeScrollVectorForPosition(targetPosition);
        }

        @Override
        protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
            return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
        }
    }
}

然后，在使用RecyclerView时，将LayoutManager设置为自定义的CustomGridLayoutManager。示例代码如下：

RecyclerView recyclerView = findViewById(R.id.recyclerView);

CustomGridLayoutManager layoutManager = new CustomGridLayoutManager(this, 2);
recyclerView.setLayoutManager(layoutManager);

// 其他设置和适配器的初始化...

// 使用smoothScrollToPosition()方法滚动到指定位置
layoutManager.smoothScrollToPosition(recyclerView, null, targetPosition);

通过自定义LayoutManager并重写smoothScrollToPosition()方法和calculateSpeedPerPixel()方法，可以调整GridLayout的smoothScrollTo()方法的滚动速度。可以根据自己的需求调整MILLISECONDS_PER_INCH的值来改变速度。