1. Whenever data changes JSON Forms will execute the validation on the whole form. For text inputs with fast typers this might lead to slowdowns, depending on how large the form is. This is something we want to fix in the long run by debouncing the input (probably within handleChange): Only apply the input, validate and emit an update change once the user stops typing for a short while. It seems you did something similar on your end to improve the performance. When using timeouts in combinations with onChange instead of onBlur you might be able to implement this yourself.
2. Make sure that JsonForms isn't fed its emitted data object again. This would trigger an expensive re-rendering including validation on each each data change (additionally to the one triggered by handleChange). We usually handle this by storing the updated form data within a useRef.

<JsonForms
schema={schema}
uischema={uischema}
data={this.state.data}
renderers={[
...materialRenderers,
{ tester: tester, renderer: CustomQuill }
]}
cells={materialCells}
onChange={this.handleChange}
/>

const debounce = (func, wait) => {
    let timeout;
    return function executedFunction(...args) {
        const later = () => {
            clearTimeout(timeout);
            func(...args);
        };
        clearTimeout(timeout);
        timeout = setTimeout(later, wait);
    };
};

<JsonForms
    schema={schema}
    uischema={uischema}
    data={standaloneData}
    renderers={[...materialRenderers]}
    cells={materialCells}
    onChange={
        denounce(
             ({({ data, errors }) => setStandaloneData(data)
        , 5000)
    }
/>

Make sure that JsonForms isn't fed its emitted data object again. This would trigger an expensive re-rendering including validation on each each data change (additionally to the one triggered by handleChange). We usually handle this by storing the updated form data within a useRef.