To me, a 15+mph speed differential is dangerous with one lane doing 55 and the other lane doing 70+. Traffic should flow together, it should blend.
Agreed! A tangential issue is what lane you are towing in. On any California multilane highway you must be in the right most (slow) lane towing except when passing or when there is a left exit. This also adds some issues when there is merging onto the road traffic. And that traffic wants to get up to 65 or 70 and you are slower. The speed differential really does not work well.
When the trucking industry wanted to go up to 80,000 gross on California highways their concession to the state was to be limited to (stay at) 55 mph. Supposedly 'slower' damages the road less when at eighteen wheeler fully loaded weights.