Indoors humidity

Hello Houston – I have a question regarding indoor humidity and thought I’ll get your thoughts and ideas.

I have a two story home with two separate HVAC units. Last year I replaced both thermostats with Nest. For the past one month I’ve noticed the upstairs humidity is consistently in the 75-79% range and the downstairs humidity is in the 55-60% range. I have verified these numbers using a separate hygrometer. Is this usual for Houston or is there something wrong that I should address? I keep both thermostats at 75 degrees. The fan runs for 15 minutes every hour. We use a vent fan when cooking and do not leave the patio/front/garage doors open. The house is south-facing and doesn’t get direct sunlight into the house from the tall windows on the back.

Should I invest in a dehumidifier at this point or are there any changes (adjust the temp, fan run time etc.) that I can do to remediate this?

Keen to see what everyone else is doing.