If slow ads were a problem, why are ad networks so damn slow? I frequently see ads taking 10–20 seconds to load on major news sites. Serving fast ads would mean more viewing time, yet that doesn't seem to be a priority for anyone.

Really? We added HTTPS to a number of ad-ridden sites and found no noticeable impact to end user page load times, page views or ad revenue.

"On our production frontend machines, SSL/TLS accounts for less than 1% of the CPU load, less than 10 KB of memory per connection and less than 2% of network overhead. Many people believe that SSL/TLS takes a lot of CPU time and we hope the preceding numbers will help to dispel that."

https://istlsfastyet.com/