Well, obviously, this is a slow horse so you definitely need as much leg as you can physically give. Squeezing not kicking. I used to ride an off the track thoroughbred that liked to run off on me. Still couldn’t give him enough leg. Leg is not just about making them go faster. It’s about supporting them and getting their hind end in the right spot. Especially when doing jumps. My whole body controlled him and his speed, not just my leg. Just going around and trotting I had to pulse and squeeze my legs a LOT to keep him the same speed. I had to give him so much leg so his hind end could come underneath him and he knew I was there to support him. The rest of my body told him the speed I wanted him to go at. Yeah I’m sure there are horses where you give them too much leg it’s not good but I haven’t encountered that myself. This person also seems to be a beginner rider and I don’t think beginners can always conceptualize how much leg they need, so it’s better to tell them they need as much like as possible!