Thank you for trying those steps, jaleisha. It's appreciated. Since reinstalling the iOS didn't resolve the issue, I'd like for you to restore your iPhone 6s and set it up as a new phone to test.
How to back up your iPhone, iPad, and iPod touch -- If you didn't back up your iPhone previously, please be sure to backup your iPhone before proceeding.
Restore your iPhone, iPad, or iPod to factory settings -- With this process, once your iPhone restarts at the end, choose to set it up as a new iPhone. Feel free to sign into iCloud and iTunes & App Store, download some of your applications and sync your information to your phone, but do not restore the backup you just created. Test the issue for a bit. If everything is working as expected, restore your iPhone again but select the backup you made to place your information back on your phone.
Apple - Support - Product Selection — If the issue happens after setting it up as a new iPhone, please contact Apple Support. After selecting this link, choose Apps & Features > The topic is not listed and use "Keyboard problems" as the issue. Then select the method you'd like to contact them with.
Cheers!