It's either what
@Falhófnir suggests, or the 16" will be a separate product that sits "above" the current MacBook Pro line, in which case I we will probably get a redesign to the 13" and 15" MacBook Pro at a different date next year and "only" the 16" this year (as per Kuo's rumors from a while ago that the rest of the lineup will be updated next year), in a similar fashion to how the iMac Pro sits above the regulars iMacs, the the 11 Pro above the iPhone 11, the coming AirPods Pro above the regular AirPods, and... well, you get the point.
It's though to say which one of the two possibilities it is, but I'm leaning towards the second one at the moment. If you compare the leaked Catalina image side-by-side with the respective image for the 15" MBP, then you'll see that the overall chassis of the 16" is actually a bit
bigger in length and width than the 15"; in other words the form factor changes and the device will be bigger (and therefore heavier) overall. The bezels are also smaller, but it's not
just the bezels that enable the screen to be bigger, it's the size of the device aswell. And I find it difficult to believe that Apple would give up the current 15" form factor that has been successful and beloved for so long in favor of a noticeably larger form factor and heavier device, which would essentially happen if Apple made the 16" the successor to the current 15". If the two devices were the exact same size on the Catalina images, then I'd agree with what
@Falhófnir's suggestion, but I'm currently leaning towards this being the "iMac Pro of MacBook Pros", rather than the next 15" MacBook Pro.
No matter which of the two it is, I don't think there will be an updated 15"
alongside the 16" this year, but for the moment I do expect a refresh/redesign to the 13" and 15" sometime next year. But we'll hopefully know more once the 16" is finally out.