Hi there,
Analytics and things like Adsense codes will require a 3rd party request, the DNS lookup and time it takes for those servers to respond are outside of your control and may vary from one minute to the next. And yes, totally the more you add the slower a site can become.
Looking at your site the Advert below the comments is centred? Did you resolve this ?
Would you be able to raise a new topic regarding the page navigation. thanks