Most people receive between 30 minutes to 2 hours of Deep sleep each night. It’s really a personal thing though. So if you are feeling fine, rest assured (so to speak).
First off, the high levels may be due to getting a lot of sleep. If this is the case, note that sleeping too much does carry some risks. In general, those who sleep more than 10 hours a night are at risk for diabetes, obesity, and depression, as well as a higher likelihood for sleep issues like Restless legs syndrome and snoring. Heightened Deep sleep levels are also a symptom of chronic fatigue syndrome.
Lifestyle factors can play a role in the amount of Deep sleep you get. High-intensity exercise during the day can significantly increase it, although more research is needed on the topic. Also, one of the side effects of ingesting cannabis, the active ingredient of which is THC, can increase Deep sleep as well as repress REM sleep (though please remember that recreational and prescription drugs have their own side effects, health problems, and legal issues).
Some medications can increase the length of Deep sleep by adjusting the neurotransmitters that structure sleep and wakefulness. Medications for depression, known as SSRIs (serotonin reuptake inhibitors) increase Deep sleep by preventing the breakdown of serotonin in the brain. Drugs replacing SSRIS like Olanzapine also can increase Deep sleep as well.