In the old days, the difference between 250 and 350 (SRW) was the springs...and nothing else. I don't know if that applies to the 2020's.
Before upgrading the springs, check:
- Tires Ratings
- Wheel Ratings
- Spring Ratings
- Axle Ratings
The lowest rating is your limit (someone will jump in if I missed a component). The first 3 are relatively simple (with cost) to upgrade. The axle can be done but it's a bit bigger of a deal.
If you want to go by the official ratings, you will be massively overweight if your payload is 2200lb. The Diesel should have no problem getting it forward but you will be squatting like nobodies business and you could be more prone to failures in the rear suspension (not necessarily instant failure but shorter life of parts)
Honestly, at 15k lb, I would be seriously looking at a dually even though some SRW trucks are technically rated for it.