A couple of things here that would make this workflow run a bit faster.
First, splitting these into two set nodes, instead of just the one, will help. In essence, you’d add another set node before the one you currently have to split up and simplify the data.
So you’d have that new Set node return two fields (one containing the value of $node["Calculate Average Speed"].json["Avg_speed"] , another one containing the value of $node["HTTP Request"].json["distances"] ).
Another important thing to do would be to use dot notation instead - like in this workflow (where the data is already split into two Set nodes for you):