It’s not 15 3/4, I went off this spec per our mechanic for 3 years and I always heard grinding and when I hit a bump it sounded like my drives were going through the trailer. You have to measure your drive tire, divide that number by 2 then add 8.75 and you’ll get your ride height within .25 +or- of that number. You have to measure in between drives at spring hanger from level ground to bottom of the frame! Once I found that out and did it I’ve had zero grinding from the ride height being to low and pushing the drive shaft into the back of the transmission!