Are you saying that adding 3/4 cup of DE raised the pressure from 15 to 16 & then after filtering awhile it went to 22?
If you haven't already done so then backwash & add some more DE.
When first using the DE I followed the instructions which were to add 1/4 cup at a time, and to continue to do so until the PSI was raised by 1. I did that and got the 1 PSI raise after (3) 1/4 cup trials. Hence I used the 3/4 cup mark as my guidline for adding DE. However, doing that caused too much drag on my system. So, this morning, after not using the DE for a while, I decided to try a small amount to see what would happen. So I used 1/4 cup diluted. That raised my PSI to about 22. Later, I added anothet 1/4 cup and that further raised the PSI to over 25. So I backwashed at that point, and got fairly dirty water. After rinsing, I added another diluted 1/4 cup to the skimmer, and am now in a holding pattern to see what happens. My take on this is that the DE helps but there is a point wherein it will be counterproductive requiring too frequent backwashing. I think the key is to find a "happy medium" where I can add a bit, without requiring frequent backwashing. Make sense??