Dovizioso stated that, "I am particularly satisfied because we improved the key point from the previous bikes, and now the bike turns in the corners." This is a reference to the old bike's tendency to understeer, a common complaint from almost everyone that rode the bike.
What's changed on the GP15? Practically everything, apparently. The previous models were all based on the original Desmosedici engine layout which saw the engine acting as the main frame; the steering head was bolted to the cylinder banks much as the Panigale is constructed now. The engine had to cope with those chassis loads, making it bigger and heavier than it would be if lodged in a traditional frame. When that big engine was eventually housed in a beam-type aluminum frame, the whole bike ended up being oversized.
Another factor partly responsible for the redesign was the engine's orientation in the chassis. The original Desmosedici was very much an "L" 90-degree layout, with the front cylinder bank almost horizontal and the rear bank almost vertical. Shortly after the switch to an aluminum frame, the team rotated the entire engine in the chassis to more of a "V" layout, presumably to improve weight balance and/or centralization. Rotating the entire engine does present a compromise, however, as this would also lower the countershaft in the chassis and make it difficult to obtain suitable anti-squat properties.
Development over the last couple of years focused on slimming the bike down to make it easier for the riders to move around on, and experimenting with weight balance and distribution; still, a total redesign was deemed necessary. Planning began almost as soon as Gigi Dall'Igna joined Ducati from Aprilia (where he designed the RSV4) in late 2013, while the GP14 was used as a test bed for concepts and ideas that would eventually see use on the GP15.
It's obvious from pictures that the new bike is significantly smaller than the old version, with a slimmer frame wrapped around what must be a more compact engine. You can see how much the engine is rotated from its original L configuration, as the rear cylinder bank now peeks out from the main frame rails above the swingarm pivot. No doubt there are new crankcases with the countershaft in the optimum position and the cylinders positioned for better weight distribution than the GP14. And even though it is a brand new bike in the early stages of development, the GP15 looks more "finished" than most of the Desmosedici iterations of the last few years.
It's early days for the GP15 yet, but the bike's strong debut does bode well for this season. One uphill battle the team may face is that Ducati, as a manufacturer that did not win a race last year, has some concessions in place as far as the Open/Factory rules structure. These concessions, which also apply to Aprilia and Suzuki as new manufacturers, are essentially identical to the benefits of the Open class - more fuel, more engines, and the softer tire option. Additionally, though, Ducati and the new manufacturers are allowed to use their own ECU software (whereas Open bikes are limited to the spec software). These rules are contingent on performance, with good results resulting in fewer concessions, even as the year goes on.
We will find out at the end of this month if the hard work of Dall'Igna and the team has paid off, when the MotoGP season begins at Losail in Qatar.