I too lost 15W for a while. When I regained it by just touching up elevation very slightly, I learned that these extremes of the arc when the dish is on a motor become tricky, especially if not using a mast in concrete. You have a mini-tower as do I. Mine is mounted on the ground on dirt. After getting the tower mast perfectly plumb one time, then touching up orientation of the dish, I can now just go to the mast at any time with a level and check that it is perfectly plumb. That bubble in my level has to be dead center with at least two measurements at right angles on the mast. If not, I correct with shims under the tower feet. Since following this, I've kept 15W and other sats solid ever since, only needing to touch up slightly on azimuth sometimes with the motor.
Since you know you had it fine one time, that simplifies life. And you know the tps are still there and strong. So just go find them!