The 14.9-24 was generally used on the LCG tractors and had a different reduction ratio to compensate for use of the smaller tire. If you change to a 28" tire you'll probably find the tractor to be quite a bit faster. That may or may not be a problem to you...
The tractor itself would probably be better with the 28" tires provided the axle reduction is appropriate.
I think you'll also find the front spindles are shorter than standard on your tractor... so if you change to 28's it's not going to sit level.