Yes, it is possible to load a JavaScript ad last on the page to prevent slow load times. One way to achieve this is by deferring the loading of the JavaScript ad until after the rest of the page content has loaded. Here are a few techniques to accomplish this:

1. Async Attribute: If the ad code is asynchronous, you can add the async attribute to the script tag. This allows the ad code to load and execute independently of the rest of the page content, without blocking the page load. For example:

<script async src="path/to/ad.js"></script>

2. Defer Attribute: If the ad code is not asynchronous, you can add the defer attribute to the script tag. This tells the browser to defer the execution of the script until after the page content has loaded. For example:

<script defer src="path/to/ad.js"></script>

3. Dynamic Script Insertion: You can use JavaScript to dynamically insert the ad code after the page content has loaded. For example:

// Wait until the page has finished loading
window.addEventListener('load', function() {
  // Create a new script element
  var adScript = document.createElement('script');
  adScript.src = 'path/to/ad.js';
  adScript.async = true;

  // Insert the script element into the document
  var targetNode = document.body || document.head || document.documentElement;
  targetNode.appendChild(adScript);
});

By loading the JavaScript ad last, you can improve the page load time and user experience by ensuring that the page content is prioritized and displayed quickly. However, keep in mind that some ad networks or ad formats may require specific loading requirements or guidelines, so it’s best to check with the ad provider before implementing any of these techniques.