I will be using SP2 = -1.5 as well.
My parameters are set according to my heater performance, overshoot.
The heater only heats until the liquid temp rises by 0.1°F, not until it reaches SP1.
Here is an example how my setup works.SP1 set to 68°F
, r2 set to 0.1°, SP2 set to -1.4°F
Heater relay #2 turns on when probe temp is below SP1+SP2-r2
or 66.5°F and off SP1+SP2 or 66.6°F
Now the heater's mass and insulation losses slowly raise the temp to the target temp of SP1 or 68°F without over shoot.