"Descended 1500 meters, or even lower" has less substantive meaning than "descended to 1500 meters, or even lower". The same is true of the other phrase contain

"Descended 1500 meters, or even lower" has less substantive meaning than "descended to 1500 meters, or even lower". The same is true of the other phrase containing the 1500 metre measure. Bad construction, but I'll assume they simply left out the 'to' in both instances.