@EricaFontimedia typically images and javascript are the primary performance issues for most websites including HubSpot. You can optimize your images by making sure the right size images are being used on the page, using the correct image format (JPG for photos, SVG for illustrations), and lazy loading images.
Javascript is a little bit harder to give advice on how to optimize without seeing the page. Your HubSpot theme may require rewriting portions of the theme to remove unnecessary dependencies such as jQuery or any other 3rd party libraries. Limiting the amount of HubSpot forms, CTAs, tracking pixels, etc… can also help improve js performance.
Hope that helps!