reduce maxSpeed to 10, update prefabs

Project/Assets/ML-Agents/Examples/Walker/Prefabs/Ragdoll/WalkerRagdollBase.prefab

     maxStep: 0
   hasUpgradedFromAgentParameters: 1
   MaxStep: 5000
-  walkingSpeed: 15
+  walkingSpeed: 10
   randomizeWalkSpeedEachEpisode: 1
   walkDirectionMethod: 0
   worldDirToWalk: {x: 1, y: 0, z: 0}

Project/Assets/ML-Agents/Examples/Walker/Scripts/WalkerAgent.cs

 
 public class WalkerAgent : Agent
 {
-    [Header("Walk Speed")] [Range(0, 15)] public float walkingSpeed = 15; //The walking speed to try and achieve
-    float m_maxWalkingSpeed = 15; //The max walking speed
+    [Header("Walk Speed")] [Range(0, 10)] public float walkingSpeed = 10; //The walking speed to try and achieve
+    float m_maxWalkingSpeed = 10; //The max walking speed
 
     //Should the agent sample a new goal velocity each episode?
     //If true, walkSpeed will be randomly set between zero and m_maxWalkingSpeed in OnEpisodeBegin()