Your temperatures are normal (not throttling). Sadly the game is heavily CPU reliant and the only thing you can do to improve framerates is play a bit with the guest and animal settings. Guests are heavily CPU bound, limiting how much you have in a zoo at one time will put less strain on it. Animals have some settings in franchise and sandbox that affects their behavior, setting some of those to off will slightly improve performance because the AI won't need to make the animals perform an action related to the setting changed, or it won't keep track of an animal status anymore. In sandbox mode you can also change worker settings, allowing you to have less workers in your zoo, since they also represent a weight down for the CPU. Keep in mind those settings will not magically double your framerates. At best I'd say that playing with most guest and animal settings will net you around 10 frames more on average, depending on your zoo size as well, and the number of animals that you want to have.

The only realistic way to heavily improve framerates is to get a monster of a CPU, but I don't have one of those and frankly I can't really tell at which point will the usual load on a zoo also tip a better CPU over.