My LT15 is a 2004 year model. The newer LT15 may have some of these also. I don't know.
Here is a list of things that the new LT28 do better or easier for me.
1. One central log clamp is fast and easy to use and it holds the boards for resaw well.
2. Power feed and return
3. Up/Down mechanism much easier and faster to operate.
4. Log turner works OK. I'm having a little problem with it but way better that not having one.
5. Toe boards work great.
6. Cuts 21' logs without an extra bed extention.
7. Ramps and winch to load logs. I will not use this much.
8. 25HP standard.
9. Trailer mounted.
10. Able to cut and easily turn bigger logs
Also, I have never been able to cut and resaw 1400BdFt in one day on my LT15. We did that the first day that we sawed with the LT28.
My LT15 did a great job for sawing logs to build my cabin and out buildings. But we are now going to be sawing mainly as a business and the LT28 will make us much more profitable for that.