Interlingua may be readily intelligible to speakers of Romance languages, but is its grammar any simpler than Esperanto's? Or is comparatively more complex and difficult to learn? Because that's what ultimately matters for the rest of the world's population who do not speak a Romance language.
Interlingua doesn’t claim to serve any community outside European language users, but it does succeed at that, I think.
Overall interlingua is about as simple and regular as can be. A Chinese speaker might still be better off learning English but I can’t imagine they’d find interlingua any harder than any natural language.
Interlingua never cared much about simplicity and regularity and it shows. Occidental before it has something called De Wahl's Rule that is focused on achieving as much regularity as possible while being easy to read at first sight. Here's how it works: https://en.wikipedia.org/wiki/De_Wahl%27s_rule#Rule