I think the biggest difference you will see is the cost.
The 1428 is a V tractor (value). Most of the 1428s, mine included, have manual transmissions. The 1528s I've seen have hydros. Personal preference on the trannys. I like the manual transmissions.
There are also some additional bells and whistles on the 1500 series like rubber mats on the operations deck and round verses square head lights.
Both are rated for 28 HP. Be careful, the ratings are at the PTO shaft...so depending on the transmission type, the HP varies.
I've had my 1428 for two plus years and have been extremely pleased with the machine. In fact yesterday it was in the 50s so it got washed and waxed.
Hope this helps.
28Red /forums/images/graemlins/cool.gif